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 <div class="section" id="built-in-functions">
<h1>2. Built-in Functions<a class="headerlink" href="#built-in-functions" title="Permalink to this headline">¶</a></h1>
The Python interpreter has a number of functions built into it that are always
available. They are listed here in alphabetical order.
<dl class="function">
<dt id="abs">
<tt class="descname">abs</tt><big>(</big>x<big>)</big><a class="headerlink" href="#abs" title="Permalink to this definition">¶</a></dt>
<dd>Return the absolute value of a number. The argument may be a plain or long
integer or a floating point number. If the argument is a complex number, its
magnitude is returned.</dd></dl>

<dl class="function">
<dt id="all">
<tt class="descname">all</tt><big>(</big>iterable<big>)</big><a class="headerlink" href="#all" title="Permalink to this definition">¶</a></dt>
<dd>Return True if all elements of the iterable are true (or if the iterable
is empty). Equivalent to:
<div class="highlight-python"><div class="highlight"><pre>def all(iterable):
 for element in iterable:
 if not element:
 return False
 return True
</pre></div>
</div>

New in version 2.5.
</dd></dl>

<dl class="function">
<dt id="any">
<tt class="descname">any</tt><big>(</big>iterable<big>)</big><a class="headerlink" href="#any" title="Permalink to this definition">¶</a></dt>
<dd>Return True if any element of the iterable is true. If the iterable
is empty, return False. Equivalent to:
<div class="highlight-python"><div class="highlight"><pre>def any(iterable):
 for element in iterable:
 if element:
 return True
 return False
</pre></div>
</div>

New in version 2.5.
</dd></dl>

<dl class="function">
<dt id="basestring">
<tt class="descname">basestring</tt><big>(</big><big>)</big><a class="headerlink" href="#basestring" title="Permalink to this definition">¶</a></dt>
<dd>This abstract type is the superclass for <a title="str" class="reference internal" href="#str"><tt class="xref docutils literal">str</tt></a> and <a title="unicode" class="reference internal" href="#unicode"><tt class="xref docutils literal">unicode</tt></a>. It
cannot be called or instantiated, but it can be used to test whether an object
is an instance of <a title="str" class="reference internal" href="#str"><tt class="xref docutils literal">str</tt></a> or <a title="unicode" class="reference internal" href="#unicode"><tt class="xref docutils literal">unicode</tt></a>. <tt class="docutils literal">isinstance(obj,
basestring)</tt> is equivalent to <tt class="docutils literal">isinstance(obj, (str, unicode))</tt>.

New in version 2.3.
</dd></dl>

<dl class="function">
<dt id="bin">
<tt class="descname">bin</tt><big>(</big>x<big>)</big><a class="headerlink" href="#bin" title="Permalink to this definition">¶</a></dt>
<dd>Convert an integer number to a binary string. The result is a valid Python
expression. If x is not a Python <a title="int" class="reference internal" href="#int"><tt class="xref docutils literal">int</tt></a> object, it has to define an
<a title="object.__index__" class="reference external" href="../reference/datamodel.html#object.__index__"><tt class="xref docutils literal">__index__()</tt></a> method that returns an integer.

New in version 2.6.
</dd></dl>

<dl class="function">
<dt id="bool">
<tt class="descname">bool</tt><big>(</big>[x]<big>)</big><a class="headerlink" href="#bool" title="Permalink to this definition">¶</a></dt>
<dd>Convert a value to a Boolean, using the standard truth testing procedure. If
x is false or omitted, this returns <a title="False" class="reference external" href="constants.html#False"><tt class="xref xref docutils literal">False</tt></a>; otherwise it returns
<a title="True" class="reference external" href="constants.html#True"><tt class="xref xref docutils literal">True</tt></a>. <a title="bool" class="reference internal" href="#bool"><tt class="xref docutils literal">bool</tt></a> is also a class, which is a subclass of
<a title="int" class="reference internal" href="#int"><tt class="xref docutils literal">int</tt></a>. Class <a title="bool" class="reference internal" href="#bool"><tt class="xref docutils literal">bool</tt></a> cannot be subclassed further. Its only
instances are <a title="False" class="reference external" href="constants.html#False"><tt class="xref xref docutils literal">False</tt></a> and <a title="True" class="reference external" href="constants.html#True"><tt class="xref xref docutils literal">True</tt></a>.

New in version 2.2.1.

Changed in version 2.3: If no argument is given, this function returns <a title="False" class="reference external" href="constants.html#False"><tt class="xref xref docutils literal">False</tt></a>.
</dd></dl>

<dl class="function">
<dt id="callable">
<tt class="descname">callable</tt><big>(</big>object<big>)</big><a class="headerlink" href="#callable" title="Permalink to this definition">¶</a></dt>
<dd>Return <a title="True" class="reference external" href="constants.html#True"><tt class="xref xref docutils literal">True</tt></a> if the object argument appears callable,
<a title="False" class="reference external" href="constants.html#False"><tt class="xref xref docutils literal">False</tt></a> if not. If this
returns true, it is still possible that a call fails, but if it is false,
calling object will never succeed. Note that classes are callable (calling a
class returns a new instance); class instances are callable if they have a
<a title="object.__call__" class="reference external" href="../reference/datamodel.html#object.__call__"><tt class="xref docutils literal">__call__()</tt></a> method.</dd></dl>

<dl class="function">
<dt id="chr">
<tt class="descname">chr</tt><big>(</big>i<big>)</big><a class="headerlink" href="#chr" title="Permalink to this definition">¶</a></dt>
<dd>Return a string of one character whose ASCII code is the integer i. For
example, <tt class="docutils literal">chr(97)</tt> returns the string <tt class="docutils literal">'a'</tt>. This is the inverse of
<a title="ord" class="reference internal" href="#ord"><tt class="xref docutils literal">ord()</tt></a>. The argument must be in the range [0..255], inclusive;
<a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal">ValueError</tt></a> will be raised if i is outside that range. See
also <a title="unichr" class="reference internal" href="#unichr"><tt class="xref docutils literal">unichr()</tt></a>.</dd></dl>

<dl class="function">
<dt id="classmethod">
<tt class="descname">classmethod</tt><big>(</big>function<big>)</big><a class="headerlink" href="#classmethod" title="Permalink to this definition">¶</a></dt>
<dd>Return a class method for function.
A class method receives the class as implicit first argument, just like an
instance method receives the instance. To declare a class method, use this
idiom:
<div class="highlight-python"><div class="highlight"><pre>class C:
 @classmethod
 def f(cls, arg1, arg2, ...): ...
</pre></div>
</div>
The <tt class="docutils literal">&#64;classmethod</tt> form is a function <a class="reference external" href="../glossary.html#term-decorator">decorator</a> &#8211; see the description
of function definitions in <a class="reference external" href="../reference/compound_stmts.html#function">Function definitions</a> for details.
It can be called either on the class (such as <tt class="docutils literal">C.f()</tt>) or on an instance (such
as <tt class="docutils literal">C().f()</tt>). The instance is ignored except for its class. If a class
method is called for a derived class, the derived class object is passed as the
implied first argument.
Class methods are different than C++ or Java static methods. If you want those,
see <a title="staticmethod" class="reference internal" href="#staticmethod"><tt class="xref docutils literal">staticmethod()</tt></a> in this section.
For more information on class methods, consult the documentation on the standard
type hierarchy in <a class="reference external" href="../reference/datamodel.html#types">The standard type hierarchy</a>.

New in version 2.2.

Changed in version 2.4: Function decorator syntax added.
</dd></dl>

<dl class="function">
<dt id="cmp">
<tt class="descname">cmp</tt><big>(</big>x, y<big>)</big><a class="headerlink" href="#cmp" title="Permalink to this definition">¶</a></dt>
<dd>Compare the two objects x and y and return an integer according to the
outcome. The return value is negative if <tt class="docutils literal">x &lt; y</tt>, zero if <tt class="docutils literal">x == y</tt> and
strictly positive if <tt class="docutils literal">x &gt; y</tt>.</dd></dl>

<dl class="function">
<dt id="compile">
<tt class="descname">compile</tt><big>(</big>source, filename, mode[, flags[, dont_inherit]]<big>)</big><a class="headerlink" href="#compile" title="Permalink to this definition">¶</a></dt>
<dd>Compile the source into a code or AST object. Code objects can be executed
by an <a class="reference external" href="../reference/simple_stmts.html#exec"><tt class="xref docutils literal">exec</tt></a> statement or evaluated by a call to <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a>.
source can either be a string or an AST object. Refer to the <a title="Abstract Syntax Tree classes and manipulation." class="reference external" href="ast.html#module-ast"><tt class="xref docutils literal">ast</tt></a>
module documentation for information on how to work with AST objects.
The filename argument should give the file from which the code was read;
pass some recognizable value if it wasn&#8217;t read from a file (<tt class="docutils literal">'&lt;string&gt;'</tt> is
commonly used).
The mode argument specifies what kind of code must be compiled; it can be
<tt class="docutils literal">'exec'</tt> if source consists of a sequence of statements, <tt class="docutils literal">'eval'</tt> if it
consists of a single expression, or <tt class="docutils literal">'single'</tt> if it consists of a single
interactive statement (in the latter case, expression statements that
evaluate to something other than <tt class="xref docutils literal">None</tt> will be printed).
The optional arguments flags and dont_inherit control which future
statements (see <a class="reference external" href="http://www.python.org/dev/peps/pep-0236">PEP 236</a>) affect the compilation of source. If neither
is present (or both are zero) the code is compiled with those future
statements that are in effect in the code that is calling compile. If the
flags argument is given and dont_inherit is not (or is zero) then the
future statements specified by the flags argument are used in addition to
those that would be used anyway. If dont_inherit is a non-zero integer then
the flags argument is it &#8211; the future statements in effect around the call
to compile are ignored.
Future statements are specified by bits which can be bitwise ORed together to
specify multiple statements. The bitfield required to specify a given feature
can be found as the <tt class="xref docutils literal">compiler_flag</tt> attribute on the <tt class="xref docutils literal">_Feature</tt>
instance in the <a title="Future statement definitions" class="reference external" href="__future__.html#module-__future__"><tt class="xref docutils literal">__future__</tt></a> module.
This function raises <a title="exceptions.SyntaxError" class="reference external" href="exceptions.html#exceptions.SyntaxError"><tt class="xref docutils literal">SyntaxError</tt></a> if the compiled source is invalid,
and <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> if the source contains null bytes.
<div class="admonition note">
Note
When compiling a string with multi-line code, line endings must be
represented by a single newline character (<tt class="docutils literal">'\n'</tt>), and the input must
be terminated by at least one newline character. If line endings are
represented by <tt class="docutils literal">'\r\n'</tt>, use <a title="str.replace" class="reference external" href="stdtypes.html#str.replace"><tt class="xref docutils literal">str.replace()</tt></a> to change them into
<tt class="docutils literal">'\n'</tt>.
</div>

Changed in version 2.3: The flags and dont_inherit arguments were added.

Changed in version 2.6: Support for compiling AST objects.
</dd></dl>

<dl class="function">
<dt id="complex">
<tt class="descname">complex</tt><big>(</big>[real[, imag]]<big>)</big><a class="headerlink" href="#complex" title="Permalink to this definition">¶</a></dt>
<dd>Create a complex number with the value real + imag*j or convert a string or
number to a complex number. If the first parameter is a string, it will be
interpreted as a complex number and the function must be called without a second
parameter. The second parameter can never be a string. Each argument may be any
numeric type (including complex). If imag is omitted, it defaults to zero and
the function serves as a numeric conversion function like <a title="int" class="reference internal" href="#int"><tt class="xref docutils literal">int()</tt></a>,
<a title="long" class="reference internal" href="#long"><tt class="xref docutils literal">long()</tt></a> and <a title="float" class="reference internal" href="#float"><tt class="xref docutils literal">float()</tt></a>. If both arguments are omitted, returns <tt class="docutils literal">0j</tt>.
The complex type is described in <a class="reference external" href="stdtypes.html#typesnumeric">Numeric Types &#8212; int, float, long, complex</a>.
</dd></dl>

<dl class="function">
<dt id="delattr">
<tt class="descname">delattr</tt><big>(</big>object, name<big>)</big><a class="headerlink" href="#delattr" title="Permalink to this definition">¶</a></dt>
<dd>This is a relative of <a title="setattr" class="reference internal" href="#setattr"><tt class="xref docutils literal">setattr()</tt></a>. The arguments are an object and a
string. The string must be the name of one of the object&#8217;s attributes. The
function deletes the named attribute, provided the object allows it. For
example, <tt class="docutils literal">delattr(x, 'foobar')</tt> is equivalent to <tt class="docutils literal">del x.foobar</tt>.</dd></dl>

<dl class="function">
<dt>
<tt class="descname">dict</tt><big>(</big>[arg]<big>)</big></dt>
<dd>Create a new data dictionary, optionally with items taken from arg.
The dictionary type is described in <a class="reference external" href="stdtypes.html#typesmapping">Mapping Types &#8212; dict</a>.
For other containers see the built in <a title="list" class="reference internal" href="#list"><tt class="xref docutils literal">list</tt></a>, <a title="set" class="reference external" href="stdtypes.html#set"><tt class="xref docutils literal">set</tt></a>, and
<a title="tuple" class="reference internal" href="#tuple"><tt class="xref docutils literal">tuple</tt></a> classes, and the <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal">collections</tt></a> module.
</dd></dl>

<dl class="function">
<dt id="dir">
<tt class="descname">dir</tt><big>(</big>[object]<big>)</big><a class="headerlink" href="#dir" title="Permalink to this definition">¶</a></dt>
<dd>Without arguments, return the list of names in the current local scope. With an
argument, attempt to return a list of valid attributes for that object.
If the object has a method named <tt class="xref docutils literal">__dir__()</tt>, this method will be called and
must return the list of attributes. This allows objects that implement a custom
<a title="object.__getattr__" class="reference external" href="../reference/datamodel.html#object.__getattr__"><tt class="xref docutils literal">__getattr__()</tt></a> or <a title="object.__getattribute__" class="reference external" href="../reference/datamodel.html#object.__getattribute__"><tt class="xref docutils literal">__getattribute__()</tt></a> function to customize the way
<a title="dir" class="reference internal" href="#dir"><tt class="xref docutils literal">dir()</tt></a> reports their attributes.
If the object does not provide <tt class="xref docutils literal">__dir__()</tt>, the function tries its best to
gather information from the object&#8217;s <tt class="xref docutils literal">__dict__</tt> attribute, if defined, and
from its type object. The resulting list is not necessarily complete, and may
be inaccurate when the object has a custom <a title="object.__getattr__" class="reference external" href="../reference/datamodel.html#object.__getattr__"><tt class="xref docutils literal">__getattr__()</tt></a>.
The default <a title="dir" class="reference internal" href="#dir"><tt class="xref docutils literal">dir()</tt></a> mechanism behaves differently with different types of
objects, as it attempts to produce the most relevant, rather than complete,
information:
<ul class="simple">
<li>If the object is a module object, the list contains the names of the module&#8217;s
attributes.</li>
<li>If the object is a type or class object, the list contains the names of its
attributes, and recursively of the attributes of its bases.</li>
<li>Otherwise, the list contains the object&#8217;s attributes&#8217; names, the names of its
class&#8217;s attributes, and recursively of the attributes of its class&#8217;s base
classes.</li>
</ul>
The resulting list is sorted alphabetically. For example:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import struct
&gt;&gt;&gt; dir() # doctest: +SKIP
[&#39;__builtins__&#39;, &#39;__doc__&#39;, &#39;__name__&#39;, &#39;struct&#39;]
&gt;&gt;&gt; dir(struct) # doctest: +NORMALIZE_WHITESPACE
[&#39;Struct&#39;, &#39;__builtins__&#39;, &#39;__doc__&#39;, &#39;__file__&#39;, &#39;__name__&#39;,
 &#39;__package__&#39;, &#39;_clearcache&#39;, &#39;calcsize&#39;, &#39;error&#39;, &#39;pack&#39;, &#39;pack_into&#39;,
 &#39;unpack&#39;, &#39;unpack_from&#39;]
&gt;&gt;&gt; class Foo(object):
... def __dir__(self):
... return [&quot;kan&quot;, &quot;ga&quot;, &quot;roo&quot;]
...
&gt;&gt;&gt; f = Foo()
&gt;&gt;&gt; dir(f)
[&#39;ga&#39;, &#39;kan&#39;, &#39;roo&#39;]
</pre></div>
</div>
<div class="admonition note">
Note
Because <a title="dir" class="reference internal" href="#dir"><tt class="xref docutils literal">dir()</tt></a> is supplied primarily as a convenience for use at an
interactive prompt, it tries to supply an interesting set of names more than it
tries to supply a rigorously or consistently defined set of names, and its
detailed behavior may change across releases. For example, metaclass attributes
are not in the result list when the argument is a class.
</div>
</dd></dl>

<dl class="function">
<dt id="divmod">
<tt class="descname">divmod</tt><big>(</big>a, b<big>)</big><a class="headerlink" href="#divmod" title="Permalink to this definition">¶</a></dt>
<dd>Take two (non complex) numbers as arguments and return a pair of numbers
consisting of their quotient and remainder when using long division. With mixed
operand types, the rules for binary arithmetic operators apply. For plain and
long integers, the result is the same as <tt class="docutils literal">(a // b, a % b)</tt>. For floating point
numbers the result is <tt class="docutils literal">(q, a % b)</tt>, where q is usually <tt class="docutils literal">math.floor(a / b)</tt>
but may be 1 less than that. In any case <tt class="docutils literal">q * b + a % b</tt> is very close to
a, if <tt class="docutils literal">a % b</tt> is non-zero it has the same sign as b, and <tt class="docutils literal">0 &lt;= abs(a % b)
&lt; abs(b)</tt>.

Changed in version 2.3: Using <a title="divmod" class="reference internal" href="#divmod"><tt class="xref docutils literal">divmod()</tt></a> with complex numbers is deprecated.
</dd></dl>

<dl class="function">
<dt id="enumerate">
<tt class="descname">enumerate</tt><big>(</big>sequence[, start=0]<big>)</big><a class="headerlink" href="#enumerate" title="Permalink to this definition">¶</a></dt>
<dd>Return an enumerate object. sequence must be a sequence, an
<a class="reference external" href="../glossary.html#term-iterator">iterator</a>, or some other object which supports iteration. The
<tt class="xref docutils literal">next()</tt> method of the iterator returned by <a title="enumerate" class="reference internal" href="#enumerate"><tt class="xref docutils literal">enumerate()</tt></a> returns a
tuple containing a count (from start which defaults to 0) and the
corresponding value obtained from iterating over iterable.
<a title="enumerate" class="reference internal" href="#enumerate"><tt class="xref docutils literal">enumerate()</tt></a> is useful for obtaining an indexed series: <tt class="docutils literal">(0, seq[0])</tt>,
<tt class="docutils literal">(1, seq[1])</tt>, <tt class="docutils literal">(2, seq[2])</tt>, .... For example:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; for i, season in enumerate([&#39;Spring&#39;, &#39;Summer&#39;, &#39;Fall&#39;, &#39;Winter&#39;]):
... print i, season
0 Spring
1 Summer
2 Fall
3 Winter
</pre></div>
</div>

New in version 2.3.

New in version 2.6: The start parameter.
</dd></dl>

<dl class="function">
<dt id="eval">
<tt class="descname">eval</tt><big>(</big>expression[, globals[, locals]]<big>)</big><a class="headerlink" href="#eval" title="Permalink to this definition">¶</a></dt>
<dd>The arguments are a string and optional globals and locals. If provided,
globals must be a dictionary. If provided, locals can be any mapping
object.

Changed in version 2.4: formerly locals was required to be a dictionary.
The expression argument is parsed and evaluated as a Python expression
(technically speaking, a condition list) using the globals and locals
dictionaries as global and local namespace. If the globals dictionary is
present and lacks &#8216;__builtins__&#8217;, the current globals are copied into globals
before expression is parsed. This means that expression normally has full
access to the standard <a title="The module that provides the built-in namespace." class="reference external" href="__builtin__.html#module-__builtin__"><tt class="xref docutils literal">__builtin__</tt></a> module and restricted environments are
propagated. If the locals dictionary is omitted it defaults to the globals
dictionary. If both dictionaries are omitted, the expression is executed in the
environment where <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a> is called. The return value is the result of
the evaluated expression. Syntax errors are reported as exceptions. Example:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; x = 1
&gt;&gt;&gt; print eval(&#39;x+1&#39;)
2
</pre></div>
</div>
This function can also be used to execute arbitrary code objects (such as
those created by <a title="compile" class="reference internal" href="#compile"><tt class="xref docutils literal">compile()</tt></a>). In this case pass a code object instead
of a string. If the code object has been compiled with <tt class="docutils literal">'exec'</tt> as the
mode argument, <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a>&#8216;s return value will be <tt class="xref docutils literal">None</tt>.
Hints: dynamic execution of statements is supported by the <a class="reference external" href="../reference/simple_stmts.html#exec"><tt class="xref docutils literal">exec</tt></a>
statement. Execution of statements from a file is supported by the
<a title="execfile" class="reference internal" href="#execfile"><tt class="xref docutils literal">execfile()</tt></a> function. The <a title="globals" class="reference internal" href="#globals"><tt class="xref docutils literal">globals()</tt></a> and <a title="locals" class="reference internal" href="#locals"><tt class="xref docutils literal">locals()</tt></a> functions
returns the current global and local dictionary, respectively, which may be
useful to pass around for use by <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a> or <a title="execfile" class="reference internal" href="#execfile"><tt class="xref docutils literal">execfile()</tt></a>.
</dd></dl>

<dl class="function">
<dt id="execfile">
<tt class="descname">execfile</tt><big>(</big>filename[, globals[, locals]]<big>)</big><a class="headerlink" href="#execfile" title="Permalink to this definition">¶</a></dt>
<dd>This function is similar to the <a class="reference external" href="../reference/simple_stmts.html#exec"><tt class="xref docutils literal">exec</tt></a> statement, but parses a file
instead of a string. It is different from the <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement in
that it does not use the module administration &#8212; it reads the file
unconditionally and does not create a new module. <a class="footnote-reference" href="#id4" id="id1">[1]</a>
The arguments are a file name and two optional dictionaries. The file is parsed
and evaluated as a sequence of Python statements (similarly to a module) using
the globals and locals dictionaries as global and local namespace. If
provided, locals can be any mapping object.

Changed in version 2.4: formerly locals was required to be a dictionary.
If the locals dictionary is omitted it defaults to the globals dictionary.
If both dictionaries are omitted, the expression is executed in the environment
where <a title="execfile" class="reference internal" href="#execfile"><tt class="xref docutils literal">execfile()</tt></a> is called. The return value is <tt class="xref docutils literal">None</tt>.
<div class="admonition note">
Note
The default locals act as described for function <a title="locals" class="reference internal" href="#locals"><tt class="xref docutils literal">locals()</tt></a> below:
modifications to the default locals dictionary should not be attempted. Pass
an explicit locals dictionary if you need to see effects of the code on
locals after function <a title="execfile" class="reference internal" href="#execfile"><tt class="xref docutils literal">execfile()</tt></a> returns. <a title="execfile" class="reference internal" href="#execfile"><tt class="xref docutils literal">execfile()</tt></a> cannot be
used reliably to modify a function&#8217;s locals.
</div>
</dd></dl>

<dl class="function">
<dt id="file">
<tt class="descname">file</tt><big>(</big>filename[, mode[, bufsize]]<big>)</big><a class="headerlink" href="#file" title="Permalink to this definition">¶</a></dt>
<dd>Constructor function for the <a title="file" class="reference internal" href="#file"><tt class="xref docutils literal">file</tt></a> type, described further in section
<a class="reference external" href="stdtypes.html#bltin-file-objects">File Objects</a>. The constructor&#8217;s arguments are the same as those
of the <a title="open" class="reference internal" href="#open"><tt class="xref docutils literal">open()</tt></a> built-in function described below.
When opening a file, it&#8217;s preferable to use <a title="open" class="reference internal" href="#open"><tt class="xref docutils literal">open()</tt></a> instead of invoking
this constructor directly. <a title="file" class="reference internal" href="#file"><tt class="xref docutils literal">file</tt></a> is more suited to type testing (for
example, writing <tt class="docutils literal">isinstance(f, file)</tt>).

New in version 2.2.
</dd></dl>

<dl class="function">
<dt id="filter">
<tt class="descname">filter</tt><big>(</big>function, iterable<big>)</big><a class="headerlink" href="#filter" title="Permalink to this definition">¶</a></dt>
<dd>Construct a list from those elements of iterable for which function returns
true. iterable may be either a sequence, a container which supports
iteration, or an iterator. If iterable is a string or a tuple, the result
also has that type; otherwise it is always a list. If function is <tt class="xref docutils literal">None</tt>,
the identity function is assumed, that is, all elements of iterable that are
false are removed.
Note that <tt class="docutils literal">filter(function, iterable)</tt> is equivalent to <tt class="docutils literal">[item for item in
iterable if function(item)]</tt> if function is not <tt class="xref docutils literal">None</tt> and <tt class="docutils literal">[item for item
in iterable if item]</tt> if function is <tt class="xref docutils literal">None</tt>.
See <a title="itertools.ifilter" class="reference external" href="itertools.html#itertools.ifilter"><tt class="xref docutils literal">itertools.ifilter()</tt></a> and <a title="itertools.ifilterfalse" class="reference external" href="itertools.html#itertools.ifilterfalse"><tt class="xref docutils literal">itertools.ifilterfalse()</tt></a> for iterator
versions of this function, including a variation that filters for elements
where the function returns false.
</dd></dl>

<dl class="function">
<dt id="float">
<tt class="descname">float</tt><big>(</big>[x]<big>)</big><a class="headerlink" href="#float" title="Permalink to this definition">¶</a></dt>
<dd>Convert a string or a number to floating point. If the argument is a string, it
must contain a possibly signed decimal or floating point number, possibly
embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf.
Otherwise, the argument may be a plain or long integer
or a floating point number, and a floating point number with the same value
(within Python&#8217;s floating point precision) is returned. If no argument is
given, returns <tt class="docutils literal">0.0</tt>.
<div class="admonition note">
Note
When passing in a string, values for NaN and Infinity may be returned, depending
on the underlying C library. Float accepts the strings nan, inf and -inf for
NaN and positive or negative infinity. The case and a leading + are ignored as
well as a leading - is ignored for NaN. Float always represents NaN and infinity
as nan, inf or -inf.
</div>
The float type is described in <a class="reference external" href="stdtypes.html#typesnumeric">Numeric Types &#8212; int, float, long, complex</a>.
</dd></dl>

<dl class="function">
<dt id="format">
<tt class="descname">format</tt><big>(</big>value[, format_spec]<big>)</big><a class="headerlink" href="#format" title="Permalink to this definition">¶</a></dt>
<dd>Convert a value to a &#8220;formatted&#8221; representation, as controlled by
format_spec. The interpretation of format_spec will depend on the type
of the value argument, however there is a standard formatting syntax that
is used by most built-in types: <a class="reference external" href="string.html#formatspec">Format Specification Mini-Language</a>.
<div class="admonition note">
Note
<tt class="docutils literal">format(value, format_spec)</tt> merely calls
<tt class="docutils literal">value.__format__(format_spec)</tt>.
</div>

New in version 2.6.
</dd></dl>

<dl class="function">
<dt>
<tt class="descname">frozenset</tt><big>(</big>[iterable]<big>)</big></dt>
<dd>Return a frozenset object, optionally with elements taken from iterable.
The frozenset type is described in <a class="reference external" href="stdtypes.html#types-set">Set Types &#8212; set, frozenset</a>.
For other containers see the built in <a title="dict" class="reference external" href="stdtypes.html#dict"><tt class="xref docutils literal">dict</tt></a>, <a title="list" class="reference internal" href="#list"><tt class="xref docutils literal">list</tt></a>, and
<a title="tuple" class="reference internal" href="#tuple"><tt class="xref docutils literal">tuple</tt></a> classes, and the <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal">collections</tt></a> module.

New in version 2.4.
</dd></dl>

<dl class="function">
<dt id="getattr">
<tt class="descname">getattr</tt><big>(</big>object, name[, default]<big>)</big><a class="headerlink" href="#getattr" title="Permalink to this definition">¶</a></dt>
<dd>Return the value of the named attributed of object. name must be a string.
If the string is the name of one of the object&#8217;s attributes, the result is the
value of that attribute. For example, <tt class="docutils literal">getattr(x, 'foobar')</tt> is equivalent to
<tt class="docutils literal">x.foobar</tt>. If the named attribute does not exist, default is returned if
provided, otherwise <a title="exceptions.AttributeError" class="reference external" href="exceptions.html#exceptions.AttributeError"><tt class="xref docutils literal">AttributeError</tt></a> is raised.</dd></dl>

<dl class="function">
<dt id="globals">
<tt class="descname">globals</tt><big>(</big><big>)</big><a class="headerlink" href="#globals" title="Permalink to this definition">¶</a></dt>
<dd>Return a dictionary representing the current global symbol table. This is always
the dictionary of the current module (inside a function or method, this is the
module where it is defined, not the module from which it is called).</dd></dl>

<dl class="function">
<dt id="hasattr">
<tt class="descname">hasattr</tt><big>(</big>object, name<big>)</big><a class="headerlink" href="#hasattr" title="Permalink to this definition">¶</a></dt>
<dd>The arguments are an object and a string. The result is <tt class="xref docutils literal">True</tt> if the string
is the name of one of the object&#8217;s attributes, <tt class="xref docutils literal">False</tt> if not. (This is
implemented by calling <tt class="docutils literal">getattr(object, name)</tt> and seeing whether it raises an
exception or not.)</dd></dl>

<dl class="function">
<dt id="hash">
<tt class="descname">hash</tt><big>(</big>object<big>)</big><a class="headerlink" href="#hash" title="Permalink to this definition">¶</a></dt>
<dd>Return the hash value of the object (if it has one). Hash values are integers.
They are used to quickly compare dictionary keys during a dictionary lookup.
Numeric values that compare equal have the same hash value (even if they are of
different types, as is the case for 1 and 1.0).</dd></dl>

<dl class="function">
<dt id="help">
<tt class="descname">help</tt><big>(</big>[object]<big>)</big><a class="headerlink" href="#help" title="Permalink to this definition">¶</a></dt>
<dd>Invoke the built-in help system. (This function is intended for interactive
use.) If no argument is given, the interactive help system starts on the
interpreter console. If the argument is a string, then the string is looked up
as the name of a module, function, class, method, keyword, or documentation
topic, and a help page is printed on the console. If the argument is any other
kind of object, a help page on the object is generated.
This function is added to the built-in namespace by the <a title="A standard way to reference site-specific modules." class="reference external" href="site.html#module-site"><tt class="xref docutils literal">site</tt></a> module.

New in version 2.2.
</dd></dl>

<dl class="function">
<dt id="hex">
<tt class="descname">hex</tt><big>(</big>x<big>)</big><a class="headerlink" href="#hex" title="Permalink to this definition">¶</a></dt>
<dd>Convert an integer number (of any size) to a hexadecimal string. The result is a
valid Python expression.
<div class="admonition note">
Note
To obtain a hexadecimal string representation for a float, use the
<a title="float.hex" class="reference external" href="stdtypes.html#float.hex"><tt class="xref docutils literal">float.hex()</tt></a> method.
</div>

Changed in version 2.4: Formerly only returned an unsigned literal.
</dd></dl>

<dl class="function">
<dt id="id">
<tt class="descname">id</tt><big>(</big>object<big>)</big><a class="headerlink" href="#id" title="Permalink to this definition">¶</a></dt>
<dd>Return the &#8220;identity&#8221; of an object. This is an integer (or long integer) which
is guaranteed to be unique and constant for this object during its lifetime.
Two objects with non-overlapping lifetimes may have the same <a title="id" class="reference internal" href="#id"><tt class="xref docutils literal">id()</tt></a>
value.
<div class="impl-detail compound">
CPython implementation detail: This is the address of the object.
</div>
</dd></dl>

<dl class="function">
<dt id="input">
<tt class="descname">input</tt><big>(</big>[prompt]<big>)</big><a class="headerlink" href="#input" title="Permalink to this definition">¶</a></dt>
<dd>Equivalent to <tt class="docutils literal">eval(raw_input(prompt))</tt>.
<div class="admonition warning">
Warning
This function is not safe from user errors! It expects a valid Python
expression as input; if the input is not syntactically valid, a
<a title="exceptions.SyntaxError" class="reference external" href="exceptions.html#exceptions.SyntaxError"><tt class="xref docutils literal">SyntaxError</tt></a> will be raised. Other exceptions may be raised if there is an
error during evaluation. (On the other hand, sometimes this is exactly what you
need when writing a quick script for expert use.)
</div>
If the <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal">readline</tt></a> module was loaded, then <a title="input" class="reference internal" href="#input"><tt class="xref docutils literal">input()</tt></a> will use it to
provide elaborate line editing and history features.
Consider using the <a title="raw_input" class="reference internal" href="#raw_input"><tt class="xref docutils literal">raw_input()</tt></a> function for general input from users.
</dd></dl>

<dl class="function">
<dt id="int">
<tt class="descname">int</tt><big>(</big>[x[, base]]<big>)</big><a class="headerlink" href="#int" title="Permalink to this definition">¶</a></dt>
<dd>Convert a string or number to a plain integer. If the argument is a string,
it must contain a possibly signed decimal number representable as a Python
integer, possibly embedded in whitespace. The base parameter gives the
base for the conversion (which is 10 by default) and may be any integer in
the range [2, 36], or zero. If base is zero, the proper radix is
determined based on the contents of string; the interpretation is the same as
for integer literals. (See <a class="reference external" href="../reference/lexical_analysis.html#numbers">Numeric literals</a>.) If base is specified and x
is not a string, <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> is raised. Otherwise, the argument may be a
plain or long integer or a floating point number. Conversion of floating
point numbers to integers truncates (towards zero). If the argument is
outside the integer range a long object will be returned instead. If no
arguments are given, returns <tt class="docutils literal">0</tt>.
The integer type is described in <a class="reference external" href="stdtypes.html#typesnumeric">Numeric Types &#8212; int, float, long, complex</a>.
</dd></dl>

<dl class="function">
<dt id="isinstance">
<tt class="descname">isinstance</tt><big>(</big>object, classinfo<big>)</big><a class="headerlink" href="#isinstance" title="Permalink to this definition">¶</a></dt>
<dd>Return true if the object argument is an instance of the classinfo argument,
or of a (direct or indirect) subclass thereof. Also return true if classinfo
is a type object (new-style class) and object is an object of that type or of
a (direct or indirect) subclass thereof. If object is not a class instance or
an object of the given type, the function always returns false. If classinfo
is neither a class object nor a type object, it may be a tuple of class or type
objects, or may recursively contain other such tuples (other sequence types are
not accepted). If classinfo is not a class, type, or tuple of classes, types,
and such tuples, a <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> exception is raised.

Changed in version 2.2: Support for a tuple of type information was added.
</dd></dl>

<dl class="function">
<dt id="issubclass">
<tt class="descname">issubclass</tt><big>(</big>class, classinfo<big>)</big><a class="headerlink" href="#issubclass" title="Permalink to this definition">¶</a></dt>
<dd>Return true if class is a subclass (direct or indirect) of classinfo. A
class is considered a subclass of itself. classinfo may be a tuple of class
objects, in which case every entry in classinfo will be checked. In any other
case, a <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> exception is raised.

Changed in version 2.3: Support for a tuple of type information was added.
</dd></dl>

<dl class="function">
<dt id="iter">
<tt class="descname">iter</tt><big>(</big>o[, sentinel]<big>)</big><a class="headerlink" href="#iter" title="Permalink to this definition">¶</a></dt>
<dd>Return an <a class="reference external" href="../glossary.html#term-iterator">iterator</a> object. The first argument is interpreted very differently
depending on the presence of the second argument. Without a second argument, o
must be a collection object which supports the iteration protocol (the
<a title="object.__iter__" class="reference external" href="../reference/datamodel.html#object.__iter__"><tt class="xref docutils literal">__iter__()</tt></a> method), or it must support the sequence protocol (the
<a title="object.__getitem__" class="reference external" href="../reference/datamodel.html#object.__getitem__"><tt class="xref docutils literal">__getitem__()</tt></a> method with integer arguments starting at <tt class="docutils literal">0</tt>). If it
does not support either of those protocols, <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> is raised. If the
second argument, sentinel, is given, then o must be a callable object. The
iterator created in this case will call o with no arguments for each call to
its <a title="iterator.next" class="reference external" href="stdtypes.html#iterator.next"><tt class="xref docutils literal">next()</tt></a> method; if the value returned is equal to sentinel,
<a title="exceptions.StopIteration" class="reference external" href="exceptions.html#exceptions.StopIteration"><tt class="xref docutils literal">StopIteration</tt></a> will be raised, otherwise the value will be returned.
One useful application of the second form of <a title="iter" class="reference internal" href="#iter"><tt class="xref docutils literal">iter()</tt></a> is to read lines of
a file until a certain line is reached. The following example reads a file
until <tt class="docutils literal">&quot;STOP&quot;</tt> is reached:
<div class="highlight-python"><div class="highlight"><pre>with open(&quot;mydata.txt&quot;) as fp:
 for line in iter(fp.readline, &quot;STOP&quot;):
 process_line(line)
</pre></div>
</div>

New in version 2.2.
</dd></dl>

<dl class="function">
<dt id="len">
<tt class="descname">len</tt><big>(</big>s<big>)</big><a class="headerlink" href="#len" title="Permalink to this definition">¶</a></dt>
<dd>Return the length (the number of items) of an object. The argument may be a
sequence (string, tuple or list) or a mapping (dictionary).</dd></dl>

<dl class="function">
<dt id="list">
<tt class="descname">list</tt><big>(</big>[iterable]<big>)</big><a class="headerlink" href="#list" title="Permalink to this definition">¶</a></dt>
<dd>Return a list whose items are the same and in the same order as iterable&#8216;s
items. iterable may be either a sequence, a container that supports
iteration, or an iterator object. If iterable is already a list, a copy is
made and returned, similar to <tt class="docutils literal">iterable[:]</tt>. For instance, <tt class="docutils literal">list('abc')</tt>
returns <tt class="docutils literal">['a', 'b', 'c']</tt> and <tt class="docutils literal">list( (1, 2, 3) )</tt> returns <tt class="docutils literal">[1, 2, 3]</tt>. If
no argument is given, returns a new empty list, <tt class="docutils literal">[]</tt>.
<a title="list" class="reference internal" href="#list"><tt class="xref docutils literal">list</tt></a> is a mutable sequence type, as documented in
<a class="reference external" href="stdtypes.html#typesseq">Sequence Types &#8212; str, unicode, list, tuple, buffer, xrange</a>. For other containers see the built in <a title="dict" class="reference external" href="stdtypes.html#dict"><tt class="xref docutils literal">dict</tt></a>,
<a title="set" class="reference external" href="stdtypes.html#set"><tt class="xref docutils literal">set</tt></a>, and <a title="tuple" class="reference internal" href="#tuple"><tt class="xref docutils literal">tuple</tt></a> classes, and the <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal">collections</tt></a> module.
</dd></dl>

<dl class="function">
<dt id="locals">
<tt class="descname">locals</tt><big>(</big><big>)</big><a class="headerlink" href="#locals" title="Permalink to this definition">¶</a></dt>
<dd>Update and return a dictionary representing the current local symbol table.
Free variables are returned by <a title="locals" class="reference internal" href="#locals"><tt class="xref docutils literal">locals()</tt></a> when it is called in function
blocks, but not in class blocks.
<div class="admonition note">
Note
The contents of this dictionary should not be modified; changes may not
affect the values of local and free variables used by the interpreter.
</div>
</dd></dl>

<dl class="function">
<dt id="long">
<tt class="descname">long</tt><big>(</big>[x[, base]]<big>)</big><a class="headerlink" href="#long" title="Permalink to this definition">¶</a></dt>
<dd>Convert a string or number to a long integer. If the argument is a string, it
must contain a possibly signed number of arbitrary size, possibly embedded in
whitespace. The base argument is interpreted in the same way as for
<a title="int" class="reference internal" href="#int"><tt class="xref docutils literal">int()</tt></a>, and may only be given when x is a string. Otherwise, the argument
may be a plain or long integer or a floating point number, and a long integer
with the same value is returned. Conversion of floating point numbers to
integers truncates (towards zero). If no arguments are given, returns <tt class="docutils literal">0L</tt>.
The long type is described in <a class="reference external" href="stdtypes.html#typesnumeric">Numeric Types &#8212; int, float, long, complex</a>.
</dd></dl>

<dl class="function">
<dt id="map">
<tt class="descname">map</tt><big>(</big>function, iterable, ...<big>)</big><a class="headerlink" href="#map" title="Permalink to this definition">¶</a></dt>
<dd>Apply function to every item of iterable and return a list of the results.
If additional iterable arguments are passed, function must take that many
arguments and is applied to the items from all iterables in parallel. If one
iterable is shorter than another it is assumed to be extended with <tt class="xref docutils literal">None</tt>
items. If function is <tt class="xref docutils literal">None</tt>, the identity function is assumed; if there
are multiple arguments, <a title="map" class="reference internal" href="#map"><tt class="xref docutils literal">map()</tt></a> returns a list consisting of tuples
containing the corresponding items from all iterables (a kind of transpose
operation). The iterable arguments may be a sequence or any iterable object;
the result is always a list.</dd></dl>

<dl class="function">
<dt id="max">
<tt class="descname">max</tt><big>(</big>iterable[, args...][, key]<big>)</big><a class="headerlink" href="#max" title="Permalink to this definition">¶</a></dt>
<dd>With a single argument iterable, return the largest item of a non-empty
iterable (such as a string, tuple or list). With more than one argument, return
the largest of the arguments.
The optional key argument specifies a one-argument ordering function like that
used for <tt class="xref docutils literal">list.sort()</tt>. The key argument, if supplied, must be in keyword
form (for example, <tt class="docutils literal">max(a,b,c,key=func)</tt>).

Changed in version 2.5: Added support for the optional key argument.
</dd></dl>

<dl class="function">
<dt id="min">
<tt class="descname">min</tt><big>(</big>iterable[, args...][, key]<big>)</big><a class="headerlink" href="#min" title="Permalink to this definition">¶</a></dt>
<dd>With a single argument iterable, return the smallest item of a non-empty
iterable (such as a string, tuple or list). With more than one argument, return
the smallest of the arguments.
The optional key argument specifies a one-argument ordering function like that
used for <tt class="xref docutils literal">list.sort()</tt>. The key argument, if supplied, must be in keyword
form (for example, <tt class="docutils literal">min(a,b,c,key=func)</tt>).

Changed in version 2.5: Added support for the optional key argument.
</dd></dl>

<dl class="function">
<dt id="next">
<tt class="descname">next</tt><big>(</big>iterator[, default]<big>)</big><a class="headerlink" href="#next" title="Permalink to this definition">¶</a></dt>
<dd>Retrieve the next item from the iterator by calling its
<a title="iterator.next" class="reference external" href="stdtypes.html#iterator.next"><tt class="xref docutils literal">next()</tt></a> method. If default is given, it is returned if the
iterator is exhausted, otherwise <a title="exceptions.StopIteration" class="reference external" href="exceptions.html#exceptions.StopIteration"><tt class="xref docutils literal">StopIteration</tt></a> is raised.

New in version 2.6.
</dd></dl>

<dl class="function">
<dt id="object">
<tt class="descname">object</tt><big>(</big><big>)</big><a class="headerlink" href="#object" title="Permalink to this definition">¶</a></dt>
<dd>Return a new featureless object. <a title="object" class="reference internal" href="#object"><tt class="xref docutils literal">object</tt></a> is a base for all new style
classes. It has the methods that are common to all instances of new style
classes.

New in version 2.2.

Changed in version 2.3: This function does not accept any arguments. Formerly, it accepted arguments but
ignored them.
</dd></dl>

<dl class="function">
<dt id="oct">
<tt class="descname">oct</tt><big>(</big>x<big>)</big><a class="headerlink" href="#oct" title="Permalink to this definition">¶</a></dt>
<dd>Convert an integer number (of any size) to an octal string. The result is a
valid Python expression.

Changed in version 2.4: Formerly only returned an unsigned literal.
</dd></dl>

<dl class="function">
<dt id="open">
<tt class="descname">open</tt><big>(</big>filename[, mode[, bufsize]]<big>)</big><a class="headerlink" href="#open" title="Permalink to this definition">¶</a></dt>
<dd>Open a file, returning an object of the <a title="file" class="reference internal" href="#file"><tt class="xref docutils literal">file</tt></a> type described in
section <a class="reference external" href="stdtypes.html#bltin-file-objects">File Objects</a>. If the file cannot be opened,
<a title="exceptions.IOError" class="reference external" href="exceptions.html#exceptions.IOError"><tt class="xref docutils literal">IOError</tt></a> is raised. When opening a file, it&#8217;s preferable to use
<a title="open" class="reference internal" href="#open"><tt class="xref docutils literal">open()</tt></a> instead of invoking the <a title="file" class="reference internal" href="#file"><tt class="xref docutils literal">file</tt></a> constructor directly.
The first two arguments are the same as for <tt class="docutils literal">stdio</tt>&#8216;s <tt class="xref docutils literal">fopen()</tt>:
filename is the file name to be opened, and mode is a string indicating how
the file is to be opened.
The most commonly-used values of mode are <tt class="docutils literal">'r'</tt> for reading, <tt class="docutils literal">'w'</tt> for
writing (truncating the file if it already exists), and <tt class="docutils literal">'a'</tt> for appending
(which on some Unix systems means that all writes append to the end of the
file regardless of the current seek position). If mode is omitted, it
defaults to <tt class="docutils literal">'r'</tt>. The default is to use text mode, which may convert
<tt class="docutils literal">'\n'</tt> characters to a platform-specific representation on writing and back
on reading. Thus, when opening a binary file, you should append <tt class="docutils literal">'b'</tt> to
the mode value to open the file in binary mode, which will improve
portability. (Appending <tt class="docutils literal">'b'</tt> is useful even on systems that don&#8217;t treat
binary and text files differently, where it serves as documentation.) See below
for more possible values of mode.
The optional bufsize argument specifies the file&#8217;s desired buffer size: 0
means unbuffered, 1 means line buffered, any other positive value means use a
buffer of (approximately) that size. A negative bufsize means to use the
system default, which is usually line buffered for tty devices and fully
buffered for other files. If omitted, the system default is used. <a class="footnote-reference" href="#id5" id="id2">[2]</a>
Modes <tt class="docutils literal">'r+'</tt>, <tt class="docutils literal">'w+'</tt> and <tt class="docutils literal">'a+'</tt> open the file for updating (note that
<tt class="docutils literal">'w+'</tt> truncates the file). Append <tt class="docutils literal">'b'</tt> to the mode to open the file in
binary mode, on systems that differentiate between binary and text files; on
systems that don&#8217;t have this distinction, adding the <tt class="docutils literal">'b'</tt> has no effect.
In addition to the standard <tt class="xref docutils literal">fopen()</tt> values mode may be <tt class="docutils literal">'U'</tt> or
<tt class="docutils literal">'rU'</tt>. Python is usually built with universal newline support; supplying
<tt class="docutils literal">'U'</tt> opens the file as a text file, but lines may be terminated by any of the
following: the Unix end-of-line convention <tt class="docutils literal">'\n'</tt>, the Macintosh convention
<tt class="docutils literal">'\r'</tt>, or the Windows convention <tt class="docutils literal">'\r\n'</tt>. All of these external
representations are seen as <tt class="docutils literal">'\n'</tt> by the Python program. If Python is built
without universal newline support a mode with <tt class="docutils literal">'U'</tt> is the same as normal
text mode. Note that file objects so opened also have an attribute called
<tt class="xref docutils literal">newlines</tt> which has a value of <tt class="xref docutils literal">None</tt> (if no newlines have yet been
seen), <tt class="docutils literal">'\n'</tt>, <tt class="docutils literal">'\r'</tt>, <tt class="docutils literal">'\r\n'</tt>, or a tuple containing all the newline
types seen.
Python enforces that the mode, after stripping <tt class="docutils literal">'U'</tt>, begins with <tt class="docutils literal">'r'</tt>,
<tt class="docutils literal">'w'</tt> or <tt class="docutils literal">'a'</tt>.
Python provides many file handling modules including
<a title="Loop over standard input or a list of files." class="reference external" href="fileinput.html#module-fileinput"><tt class="xref docutils literal">fileinput</tt></a>, <a title="Miscellaneous operating system interfaces." class="reference external" href="os.html#module-os"><tt class="xref docutils literal">os</tt></a>, <a title="Operations on pathnames." class="reference external" href="os.path.html#module-os.path"><tt class="xref docutils literal">os.path</tt></a>, <a title="Generate temporary files and directories." class="reference external" href="tempfile.html#module-tempfile"><tt class="xref docutils literal">tempfile</tt></a>, and
<a title="High-level file operations, including copying." class="reference external" href="shutil.html#module-shutil"><tt class="xref docutils literal">shutil</tt></a>.

Changed in version 2.5: Restriction on first letter of mode string introduced.
</dd></dl>

<dl class="function">
<dt id="ord">
<tt class="descname">ord</tt><big>(</big>c<big>)</big><a class="headerlink" href="#ord" title="Permalink to this definition">¶</a></dt>
<dd>Given a string of length one, return an integer representing the Unicode code
point of the character when the argument is a unicode object, or the value of
the byte when the argument is an 8-bit string. For example, <tt class="docutils literal">ord('a')</tt> returns
the integer <tt class="docutils literal">97</tt>, <tt class="docutils literal">ord(u'\u2020')</tt> returns <tt class="docutils literal">8224</tt>. This is the inverse of
<a title="chr" class="reference internal" href="#chr"><tt class="xref docutils literal">chr()</tt></a> for 8-bit strings and of <a title="unichr" class="reference internal" href="#unichr"><tt class="xref docutils literal">unichr()</tt></a> for unicode objects. If a
unicode argument is given and Python was built with UCS2 Unicode, then the
character&#8217;s code point must be in the range [0..65535] inclusive; otherwise the
string length is two, and a <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> will be raised.</dd></dl>

<dl class="function">
<dt id="pow">
<tt class="descname">pow</tt><big>(</big>x, y[, z]<big>)</big><a class="headerlink" href="#pow" title="Permalink to this definition">¶</a></dt>
<dd>Return x to the power y; if z is present, return x to the power y,
modulo z (computed more efficiently than <tt class="docutils literal">pow(x, y) % z</tt>). The two-argument
form <tt class="docutils literal">pow(x, y)</tt> is equivalent to using the power operator: <tt class="docutils literal">x**y</tt>.
The arguments must have numeric types. With mixed operand types, the coercion
rules for binary arithmetic operators apply. For int and long int operands, the
result has the same type as the operands (after coercion) unless the second
argument is negative; in that case, all arguments are converted to float and a
float result is delivered. For example, <tt class="docutils literal">10**2</tt> returns <tt class="docutils literal">100</tt>, but
<tt class="docutils literal">10**-2</tt> returns <tt class="docutils literal">0.01</tt>. (This last feature was added in Python 2.2. In
Python 2.1 and before, if both arguments were of integer types and the second
argument was negative, an exception was raised.) If the second argument is
negative, the third argument must be omitted. If z is present, x and y
must be of integer types, and y must be non-negative. (This restriction was
added in Python 2.2. In Python 2.1 and before, floating 3-argument <tt class="docutils literal">pow()</tt>
returned platform-dependent results depending on floating-point rounding
accidents.)
</dd></dl>

<dl class="function">
<dt id="print">
<tt class="descname">print</tt><big>(</big>[object, ...][, sep=' '][, end='\n'][, file=sys.stdout]<big>)</big><a class="headerlink" href="#print" title="Permalink to this definition">¶</a></dt>
<dd>Print object(s) to the stream file, separated by sep and followed by
end. sep, end and file, if present, must be given as keyword
arguments.
All non-keyword arguments are converted to strings like <a title="str" class="reference internal" href="#str"><tt class="xref docutils literal">str()</tt></a> does and
written to the stream, separated by sep and followed by end. Both sep
and end must be strings; they can also be <tt class="xref docutils literal">None</tt>, which means to use the
default values. If no object is given, <a title="print" class="reference internal" href="#print"><tt class="xref docutils literal">print()</tt></a> will just write
end.
The file argument must be an object with a <tt class="docutils literal">write(string)</tt> method; if it
is not present or <tt class="xref docutils literal">None</tt>, <a title="sys.stdout" class="reference external" href="sys.html#sys.stdout"><tt class="xref docutils literal">sys.stdout</tt></a> will be used.
<div class="admonition note">
Note
This function is not normally available as a built-in since the name
<tt class="docutils literal">print</tt> is recognized as the <a class="reference external" href="../reference/simple_stmts.html#print"><tt class="xref docutils literal">print</tt></a> statement. To disable the
statement and use the <a title="print" class="reference internal" href="#print"><tt class="xref docutils literal">print()</tt></a> function, use this future statement at
the top of your module:
<div class="last highlight-python"><div class="highlight"><pre>from __future__ import print_function
</pre></div>
</div>
</div>

New in version 2.6.
</dd></dl>

<dl class="function">
<dt id="property">
<tt class="descname">property</tt><big>(</big>[fget[, fset[, fdel[, doc]]]]<big>)</big><a class="headerlink" href="#property" title="Permalink to this definition">¶</a></dt>
<dd>Return a property attribute for <a class="reference external" href="../glossary.html#term-new-style-class">new-style class</a>es (classes that
derive from <a title="object" class="reference internal" href="#object"><tt class="xref docutils literal">object</tt></a>).
fget is a function for getting an attribute value, likewise fset is a
function for setting, and fdel a function for del&#8217;ing, an attribute. Typical
use is to define a managed attribute <tt class="docutils literal">x</tt>:
<div class="highlight-python"><div class="highlight"><pre>class C(object):
 def __init__(self):
 self._x = None

def getx(self):
 return self._x
 def setx(self, value):
 self._x = value
 def delx(self):
 del self._x
 x = property(getx, setx, delx, &quot;I&#39;m the &#39;x&#39; property.&quot;)
</pre></div>
</div>
If then c is an instance of C, <tt class="docutils literal">c.x</tt> will invoke the getter,
<tt class="docutils literal">c.x = value</tt> will invoke the setter and <tt class="docutils literal">del c.x</tt> the deleter.
If given, doc will be the docstring of the property attribute. Otherwise, the
property will copy fget&#8216;s docstring (if it exists). This makes it possible to
create read-only properties easily using <a title="property" class="reference internal" href="#property"><tt class="xref docutils literal">property()</tt></a> as a <a class="reference external" href="../glossary.html#term-decorator">decorator</a>:
<div class="highlight-python"><div class="highlight"><pre>class Parrot(object):
 def __init__(self):
 self._voltage = 100000

@property
 def voltage(self):
 &quot;&quot;&quot;Get the current voltage.&quot;&quot;&quot;
 return self._voltage
</pre></div>
</div>
turns the <tt class="xref docutils literal">voltage()</tt> method into a &#8220;getter&#8221; for a read-only attribute
with the same name.
A property object has <tt class="xref docutils literal">getter</tt>, <tt class="xref docutils literal">setter</tt>, and <tt class="xref docutils literal">deleter</tt>
methods usable as decorators that create a copy of the property with the
corresponding accessor function set to the decorated function. This is
best explained with an example:
<div class="highlight-python"><div class="highlight"><pre>class C(object):
 def __init__(self):
 self._x = None

@property
 def x(self):
 &quot;&quot;&quot;I&#39;m the &#39;x&#39; property.&quot;&quot;&quot;
 return self._x

@x.setter
 def x(self, value):
 self._x = value

@x.deleter
 def x(self):
 del self._x
</pre></div>
</div>
This code is exactly equivalent to the first example. Be sure to give the
additional functions the same name as the original property (<tt class="docutils literal">x</tt> in this
case.)
The returned property also has the attributes <tt class="docutils literal">fget</tt>, <tt class="docutils literal">fset</tt>, and
<tt class="docutils literal">fdel</tt> corresponding to the constructor arguments.

New in version 2.2.

Changed in version 2.5: Use fget&#8216;s docstring if no doc given.

Changed in version 2.6: The <tt class="docutils literal">getter</tt>, <tt class="docutils literal">setter</tt>, and <tt class="docutils literal">deleter</tt> attributes were added.
</dd></dl>

<dl class="function">
<dt id="range">
<tt class="descname">range</tt><big>(</big>[start], stop[, step]<big>)</big><a class="headerlink" href="#range" title="Permalink to this definition">¶</a></dt>
<dd>This is a versatile function to create lists containing arithmetic progressions.
It is most often used in <a class="reference external" href="../reference/compound_stmts.html#for"><tt class="xref docutils literal">for</tt></a> loops. The arguments must be plain
integers. If the step argument is omitted, it defaults to <tt class="docutils literal">1</tt>. If the
start argument is omitted, it defaults to <tt class="docutils literal">0</tt>. The full form returns a list
of plain integers <tt class="docutils literal">[start, start + step, start + 2 * step, ...]</tt>. If step
is positive, the last element is the largest <tt class="docutils literal">start + i * step</tt> less than
stop; if step is negative, the last element is the smallest <tt class="docutils literal">start + i *
step</tt> greater than stop. step must not be zero (or else <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal">ValueError</tt></a>
is raised). Example:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
&gt;&gt;&gt; range(1, 11)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
&gt;&gt;&gt; range(0, 30, 5)
[0, 5, 10, 15, 20, 25]
&gt;&gt;&gt; range(0, 10, 3)
[0, 3, 6, 9]
&gt;&gt;&gt; range(0, -10, -1)
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
&gt;&gt;&gt; range(0)
[]
&gt;&gt;&gt; range(1, 0)
[]
</pre></div>
</div>
</dd></dl>

<dl class="function">
<dt id="raw_input">
<tt class="descname">raw_input</tt><big>(</big>[prompt]<big>)</big><a class="headerlink" href="#raw_input" title="Permalink to this definition">¶</a></dt>
<dd>If the prompt argument is present, it is written to standard output without a
trailing newline. The function then reads a line from input, converts it to a
string (stripping a trailing newline), and returns that. When EOF is read,
<a title="exceptions.EOFError" class="reference external" href="exceptions.html#exceptions.EOFError"><tt class="xref docutils literal">EOFError</tt></a> is raised. Example:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; s = raw_input(&#39;--&gt; &#39;)
--&gt; Monty Python&#39;s Flying Circus
&gt;&gt;&gt; s
&quot;Monty Python&#39;s Flying Circus&quot;
</pre></div>
</div>
If the <a title="(Unix) GNU readline support for Python." class="reference external" href="readline.html#module-readline"><tt class="xref docutils literal">readline</tt></a> module was loaded, then <a title="raw_input" class="reference internal" href="#raw_input"><tt class="xref docutils literal">raw_input()</tt></a> will use it to
provide elaborate line editing and history features.
</dd></dl>

<dl class="function">
<dt id="reduce">
<tt class="descname">reduce</tt><big>(</big>function, iterable[, initializer]<big>)</big><a class="headerlink" href="#reduce" title="Permalink to this definition">¶</a></dt>
<dd>Apply function of two arguments cumulatively to the items of iterable, from
left to right, so as to reduce the iterable to a single value. For example,
<tt class="docutils literal">reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])</tt> calculates <tt class="docutils literal">((((1+2)+3)+4)+5)</tt>.
The left argument, x, is the accumulated value and the right argument, y, is
the update value from the iterable. If the optional initializer is present,
it is placed before the items of the iterable in the calculation, and serves as
a default when the iterable is empty. If initializer is not given and
iterable contains only one item, the first item is returned.</dd></dl>

<dl class="function">
<dt id="reload">
<tt class="descname">reload</tt><big>(</big>module<big>)</big><a class="headerlink" href="#reload" title="Permalink to this definition">¶</a></dt>
<dd>Reload a previously imported module. The argument must be a module object, so
it must have been successfully imported before. This is useful if you have
edited the module source file using an external editor and want to try out the
new version without leaving the Python interpreter. The return value is the
module object (the same as the module argument).
When <tt class="docutils literal">reload(module)</tt> is executed:
<ul class="simple">
<li>Python modules&#8217; code is recompiled and the module-level code reexecuted,
defining a new set of objects which are bound to names in the module&#8217;s
dictionary. The <tt class="docutils literal">init</tt> function of extension modules is not called a second
time.</li>
<li>As with all other objects in Python the old objects are only reclaimed after
their reference counts drop to zero.</li>
<li>The names in the module namespace are updated to point to any new or changed
objects.</li>
<li>Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.</li>
</ul>
There are a number of other caveats:
If a module is syntactically correct but its initialization fails, the first
<a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement for it does not bind its name locally, but does
store a (partially initialized) module object in <tt class="docutils literal">sys.modules</tt>. To reload the
module you must first <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> it again (this will bind the name to the
partially initialized module object) before you can <a title="reload" class="reference internal" href="#reload"><tt class="xref docutils literal">reload()</tt></a> it.
When a module is reloaded, its dictionary (containing the module&#8217;s global
variables) is retained. Redefinitions of names will override the old
definitions, so this is generally not a problem. If the new version of a module
does not define a name that was defined by the old version, the old definition
remains. This feature can be used to the module&#8217;s advantage if it maintains a
global table or cache of objects &#8212; with a <a class="reference external" href="../reference/compound_stmts.html#try"><tt class="xref docutils literal">try</tt></a> statement it can test
for the table&#8217;s presence and skip its initialization if desired:
<div class="highlight-python"><div class="highlight"><pre>try:
 cache
except NameError:
 cache = {}
</pre></div>
</div>
It is legal though generally not very useful to reload built-in or dynamically
loaded modules, except for <a title="Access system-specific parameters and functions." class="reference external" href="sys.html#module-sys"><tt class="xref docutils literal">sys</tt></a>, <a title="The environment where the top-level script is run." class="reference external" href="__main__.html#module-__main__"><tt class="xref docutils literal">__main__</tt></a> and <a title="The module that provides the built-in namespace." class="reference external" href="__builtin__.html#module-__builtin__"><tt class="xref docutils literal">__builtin__</tt></a>.
In many cases, however, extension modules are not designed to be initialized
more than once, and may fail in arbitrary ways when reloaded.
If a module imports objects from another module using <a class="reference external" href="../reference/simple_stmts.html#from"><tt class="xref docutils literal">from</tt></a> ...
<a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> ..., calling <a title="reload" class="reference internal" href="#reload"><tt class="xref docutils literal">reload()</tt></a> for the other module does not
redefine the objects imported from it &#8212; one way around this is to re-execute
the <a class="reference external" href="../reference/simple_stmts.html#from"><tt class="xref docutils literal">from</tt></a> statement, another is to use <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> and qualified
names (module.*name*) instead.
If a module instantiates instances of a class, reloading the module that defines
the class does not affect the method definitions of the instances &#8212; they
continue to use the old class definition. The same is true for derived classes.
</dd></dl>

<dl class="function">
<dt id="repr">
<tt class="descname">repr</tt><big>(</big>object<big>)</big><a class="headerlink" href="#repr" title="Permalink to this definition">¶</a></dt>
<dd>Return a string containing a printable representation of an object. This is
the same value yielded by conversions (reverse quotes). It is sometimes
useful to be able to access this operation as an ordinary function. For many
types, this function makes an attempt to return a string that would yield an
object with the same value when passed to <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a>, otherwise the
representation is a string enclosed in angle brackets that contains the name
of the type of the object together with additional information often
including the name and address of the object. A class can control what this
function returns for its instances by defining a <a title="object.__repr__" class="reference external" href="../reference/datamodel.html#object.__repr__"><tt class="xref docutils literal">__repr__()</tt></a> method.</dd></dl>

<dl class="function">
<dt id="reversed">
<tt class="descname">reversed</tt><big>(</big>seq<big>)</big><a class="headerlink" href="#reversed" title="Permalink to this definition">¶</a></dt>
<dd>Return a reverse <a class="reference external" href="../glossary.html#term-iterator">iterator</a>. seq must be an object which has
a <a title="object.__reversed__" class="reference external" href="../reference/datamodel.html#object.__reversed__"><tt class="xref docutils literal">__reversed__()</tt></a> method or supports the sequence protocol (the
<a title="object.__len__" class="reference external" href="../reference/datamodel.html#object.__len__"><tt class="xref docutils literal">__len__()</tt></a> method and the <a title="object.__getitem__" class="reference external" href="../reference/datamodel.html#object.__getitem__"><tt class="xref docutils literal">__getitem__()</tt></a> method with integer
arguments starting at <tt class="docutils literal">0</tt>).

New in version 2.4.

Changed in version 2.6: Added the possibility to write a custom <a title="object.__reversed__" class="reference external" href="../reference/datamodel.html#object.__reversed__"><tt class="xref docutils literal">__reversed__()</tt></a> method.
</dd></dl>

<dl class="function">
<dt id="round">
<tt class="descname">round</tt><big>(</big>x[, n]<big>)</big><a class="headerlink" href="#round" title="Permalink to this definition">¶</a></dt>
<dd>Return the floating point value x rounded to n digits after the decimal
point. If n is omitted, it defaults to zero. The result is a floating point
number. Values are rounded to the closest multiple of 10 to the power minus
n; if two multiples are equally close, rounding is done away from 0 (so. for
example, <tt class="docutils literal">round(0.5)</tt> is <tt class="docutils literal">1.0</tt> and <tt class="docutils literal">round(-0.5)</tt> is <tt class="docutils literal">-1.0</tt>).</dd></dl>

<dl class="function">
<dt>
<tt class="descname">set</tt><big>(</big>[iterable]<big>)</big></dt>
<dd>Return a new set, optionally with elements taken from iterable.
The set type is described in <a class="reference external" href="stdtypes.html#types-set">Set Types &#8212; set, frozenset</a>.
For other containers see the built in <a title="dict" class="reference external" href="stdtypes.html#dict"><tt class="xref docutils literal">dict</tt></a>, <a title="list" class="reference internal" href="#list"><tt class="xref docutils literal">list</tt></a>, and
<a title="tuple" class="reference internal" href="#tuple"><tt class="xref docutils literal">tuple</tt></a> classes, and the <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal">collections</tt></a> module.

New in version 2.4.
</dd></dl>

<dl class="function">
<dt id="setattr">
<tt class="descname">setattr</tt><big>(</big>object, name, value<big>)</big><a class="headerlink" href="#setattr" title="Permalink to this definition">¶</a></dt>
<dd>This is the counterpart of <a title="getattr" class="reference internal" href="#getattr"><tt class="xref docutils literal">getattr()</tt></a>. The arguments are an object, a
string and an arbitrary value. The string may name an existing attribute or a
new attribute. The function assigns the value to the attribute, provided the
object allows it. For example, <tt class="docutils literal">setattr(x, 'foobar', 123)</tt> is equivalent to
<tt class="docutils literal">x.foobar = 123</tt>.</dd></dl>

<dl class="function">
<dt id="slice">
<tt class="descname">slice</tt><big>(</big>[start], stop[, step]<big>)</big><a class="headerlink" href="#slice" title="Permalink to this definition">¶</a></dt>
<dd>Return a <a class="reference external" href="../glossary.html#term-slice">slice</a> object representing the set of indices specified by
<tt class="docutils literal">range(start, stop, step)</tt>. The start and step arguments default to
<tt class="xref docutils literal">None</tt>. Slice objects have read-only data attributes <tt class="xref docutils literal">start</tt>,
<tt class="xref docutils literal">stop</tt> and <tt class="xref docutils literal">step</tt> which merely return the argument values (or their
default). They have no other explicit functionality; however they are used by
Numerical Python and other third party extensions. Slice objects are also
generated when extended indexing syntax is used. For example:
<tt class="docutils literal">a[start:stop:step]</tt> or <tt class="docutils literal">a[start:stop, i]</tt>. See <a title="itertools.islice" class="reference external" href="itertools.html#itertools.islice"><tt class="xref docutils literal">itertools.islice()</tt></a>
for an alternate version that returns an iterator.
</dd></dl>

<dl class="function">
<dt id="sorted">
<tt class="descname">sorted</tt><big>(</big>iterable[, cmp[, key[, reverse]]]<big>)</big><a class="headerlink" href="#sorted" title="Permalink to this definition">¶</a></dt>
<dd>Return a new sorted list from the items in iterable.
The optional arguments cmp, key, and reverse have the same meaning as
those for the <tt class="xref docutils literal">list.sort()</tt> method (described in section
<a class="reference external" href="stdtypes.html#typesseq-mutable">Mutable Sequence Types</a>).
cmp specifies a custom comparison function of two arguments (iterable
elements) which should return a negative, zero or positive number depending on
whether the first argument is considered smaller than, equal to, or larger than
the second argument: <tt class="docutils literal">cmp=lambda x,y: cmp(x.lower(), y.lower())</tt>. The default
value is <tt class="xref docutils literal">None</tt>.
key specifies a function of one argument that is used to extract a comparison
key from each list element: <tt class="docutils literal">key=str.lower</tt>. The default value is <tt class="xref docutils literal">None</tt>
(compare the elements directly).
reverse is a boolean value. If set to <tt class="xref docutils literal">True</tt>, then the list elements are
sorted as if each comparison were reversed.
In general, the key and reverse conversion processes are much faster
than specifying an equivalent cmp function. This is because cmp is
called multiple times for each list element while key and reverse touch
each element only once. To convert an old-style cmp function to a key
function, see the <a class="reference external" href="http://code.activestate.com/recipes/576653/">CmpToKey recipe in the ASPN cookbook</a>.
For sorting examples and a brief sorting tutorial, see <a class="reference external" href="http://wiki.python.org/moin/HowTo/Sorting/">Sorting HowTo</a>.

New in version 2.4.
</dd></dl>

<dl class="function">
<dt id="staticmethod">
<tt class="descname">staticmethod</tt><big>(</big>function<big>)</big><a class="headerlink" href="#staticmethod" title="Permalink to this definition">¶</a></dt>
<dd>Return a static method for function.
A static method does not receive an implicit first argument. To declare a static
method, use this idiom:
<div class="highlight-python"><div class="highlight"><pre>class C:
 @staticmethod
 def f(arg1, arg2, ...): ...
</pre></div>
</div>
The <tt class="docutils literal">&#64;staticmethod</tt> form is a function <a class="reference external" href="../glossary.html#term-decorator">decorator</a> &#8211; see the
description of function definitions in <a class="reference external" href="../reference/compound_stmts.html#function">Function definitions</a> for details.
It can be called either on the class (such as <tt class="docutils literal">C.f()</tt>) or on an instance (such
as <tt class="docutils literal">C().f()</tt>). The instance is ignored except for its class.
Static methods in Python are similar to those found in Java or C++. For a more
advanced concept, see <a title="classmethod" class="reference internal" href="#classmethod"><tt class="xref docutils literal">classmethod()</tt></a> in this section.
For more information on static methods, consult the documentation on the
standard type hierarchy in <a class="reference external" href="../reference/datamodel.html#types">The standard type hierarchy</a>.

New in version 2.2.

Changed in version 2.4: Function decorator syntax added.
</dd></dl>

<dl class="function">
<dt id="str">
<tt class="descname">str</tt><big>(</big>[object]<big>)</big><a class="headerlink" href="#str" title="Permalink to this definition">¶</a></dt>
<dd>Return a string containing a nicely printable representation of an object. For
strings, this returns the string itself. The difference with <tt class="docutils literal">repr(object)</tt>
is that <tt class="docutils literal">str(object)</tt> does not always attempt to return a string that is
acceptable to <a title="eval" class="reference internal" href="#eval"><tt class="xref docutils literal">eval()</tt></a>; its goal is to return a printable string. If no
argument is given, returns the empty string, <tt class="docutils literal">''</tt>.
For more information on strings see <a class="reference external" href="stdtypes.html#typesseq">Sequence Types &#8212; str, unicode, list, tuple, buffer, xrange</a> which describes sequence
functionality (strings are sequences), and also the string-specific methods
described in the <a class="reference external" href="stdtypes.html#string-methods">String Methods</a> section. To output formatted strings
use template strings or the <tt class="docutils literal">%</tt> operator described in the
<a class="reference external" href="stdtypes.html#string-formatting">String Formatting Operations</a> section. In addition see the <a class="reference external" href="strings.html#stringservices">String Services</a>
section. See also <a title="unicode" class="reference internal" href="#unicode"><tt class="xref docutils literal">unicode()</tt></a>.
</dd></dl>

<dl class="function">
<dt id="sum">
<tt class="descname">sum</tt><big>(</big>iterable[, start]<big>)</big><a class="headerlink" href="#sum" title="Permalink to this definition">¶</a></dt>
<dd>Sums start and the items of an iterable from left to right and returns the
total. start defaults to <tt class="docutils literal">0</tt>. The iterable&#8216;s items are normally numbers,
and are not allowed to be strings. The fast, correct way to concatenate a
sequence of strings is by calling <tt class="docutils literal">''.join(sequence)</tt>. Note that
<tt class="docutils literal">sum(range(n), m)</tt> is equivalent to <tt class="docutils literal">reduce(operator.add, range(n), m)</tt>
To add floating point values with extended precision, see <a title="math.fsum" class="reference external" href="math.html#math.fsum"><tt class="xref docutils literal">math.fsum()</tt></a>.

New in version 2.3.
</dd></dl>

<dl class="function">
<dt id="super">
<tt class="descname">super</tt><big>(</big>type[, object-or-type]<big>)</big><a class="headerlink" href="#super" title="Permalink to this definition">¶</a></dt>
<dd>Return a proxy object that delegates method calls to a parent or sibling
class of type. This is useful for accessing inherited methods that have
been overridden in a class. The search order is same as that used by
<a title="getattr" class="reference internal" href="#getattr"><tt class="xref docutils literal">getattr()</tt></a> except that the type itself is skipped.
The <tt class="xref docutils literal">__mro__</tt> attribute of the type lists the method resolution
search order used by both <a title="getattr" class="reference internal" href="#getattr"><tt class="xref docutils literal">getattr()</tt></a> and <a title="super" class="reference internal" href="#super"><tt class="xref docutils literal">super()</tt></a>. The attribute
is dynamic and can change whenever the inheritance hierarchy is updated.
If the second argument is omitted, the super object returned is unbound. If
the second argument is an object, <tt class="docutils literal">isinstance(obj, type)</tt> must be true. If
the second argument is a type, <tt class="docutils literal">issubclass(type2, type)</tt> must be true (this
is useful for classmethods).
<div class="admonition note">
Note
<a title="super" class="reference internal" href="#super"><tt class="xref docutils literal">super()</tt></a> only works for <a class="reference external" href="../glossary.html#term-new-style-class">new-style class</a>es.
</div>
There are two typical use cases for super. In a class hierarchy with
single inheritance, super can be used to refer to parent classes without
naming them explicitly, thus making the code more maintainable. This use
closely parallels the use of super in other programming languages.
The second use case is to support cooperative multiple inheritance in a
dynamic execution environment. This use case is unique to Python and is
not found in statically compiled languages or languages that only support
single inheritance. This makes it possible to implement &#8220;diamond diagrams&#8221;
where multiple base classes implement the same method. Good design dictates
that this method have the same calling signature in every case (because the
order of calls is determined at runtime, because that order adapts
to changes in the class hierarchy, and because that order can include
sibling classes that are unknown prior to runtime).
For both use cases, a typical superclass call looks like this:
<div class="highlight-python"><div class="highlight"><pre>class C(B):
 def method(self, arg):
 super(C, self).method(arg)
</pre></div>
</div>
Note that <a title="super" class="reference internal" href="#super"><tt class="xref docutils literal">super()</tt></a> is implemented as part of the binding process for
explicit dotted attribute lookups such as <tt class="docutils literal">super().__getitem__(name)</tt>.
It does so by implementing its own <a title="object.__getattribute__" class="reference external" href="../reference/datamodel.html#object.__getattribute__"><tt class="xref docutils literal">__getattribute__()</tt></a> method for searching
classes in a predictable order that supports cooperative multiple inheritance.
Accordingly, <a title="super" class="reference internal" href="#super"><tt class="xref docutils literal">super()</tt></a> is undefined for implicit lookups using statements or
operators such as <tt class="docutils literal">super()[name]</tt>.
Also note that <a title="super" class="reference internal" href="#super"><tt class="xref docutils literal">super()</tt></a> is not limited to use inside methods. The two
argument form specifies the arguments exactly and makes the appropriate
references.

New in version 2.2.
</dd></dl>

<dl class="function">
<dt id="tuple">
<tt class="descname">tuple</tt><big>(</big>[iterable]<big>)</big><a class="headerlink" href="#tuple" title="Permalink to this definition">¶</a></dt>
<dd>Return a tuple whose items are the same and in the same order as iterable&#8216;s
items. iterable may be a sequence, a container that supports iteration, or an
iterator object. If iterable is already a tuple, it is returned unchanged.
For instance, <tt class="docutils literal">tuple('abc')</tt> returns <tt class="docutils literal">('a', 'b', 'c')</tt> and <tt class="docutils literal">tuple([1, 2,
3])</tt> returns <tt class="docutils literal">(1, 2, 3)</tt>. If no argument is given, returns a new empty
tuple, <tt class="docutils literal">()</tt>.
<a title="tuple" class="reference internal" href="#tuple"><tt class="xref docutils literal">tuple</tt></a> is an immutable sequence type, as documented in
<a class="reference external" href="stdtypes.html#typesseq">Sequence Types &#8212; str, unicode, list, tuple, buffer, xrange</a>. For other containers see the built in <a title="dict" class="reference external" href="stdtypes.html#dict"><tt class="xref docutils literal">dict</tt></a>,
<a title="list" class="reference internal" href="#list"><tt class="xref docutils literal">list</tt></a>, and <a title="set" class="reference external" href="stdtypes.html#set"><tt class="xref docutils literal">set</tt></a> classes, and the <a title="High-performance datatypes" class="reference external" href="collections.html#module-collections"><tt class="xref docutils literal">collections</tt></a> module.
</dd></dl>

<dl class="function">
<dt id="type">
<tt class="descname">type</tt><big>(</big>object<big>)</big><a class="headerlink" href="#type" title="Permalink to this definition">¶</a></dt>
<dd>Return the type of an object. The return value is a type object. The
<a title="isinstance" class="reference internal" href="#isinstance"><tt class="xref docutils literal">isinstance()</tt></a> built-in function is recommended for testing the type of an
object.
With three arguments, <a title="type" class="reference internal" href="#type"><tt class="xref docutils literal">type()</tt></a> functions as a constructor as detailed below.
</dd></dl>

<dl class="function">
<dt>
<tt class="descname">type</tt><big>(</big>name, bases, dict<big>)</big></dt>
<dd>Return a new type object. This is essentially a dynamic form of the
<a class="reference external" href="../reference/compound_stmts.html#class"><tt class="xref docutils literal">class</tt></a> statement. The name string is the class name and becomes the
<tt class="xref docutils literal">__name__</tt> attribute; the bases tuple itemizes the base classes and
becomes the <tt class="xref docutils literal">__bases__</tt> attribute; and the dict dictionary is the
namespace containing definitions for class body and becomes the <tt class="xref docutils literal">__dict__</tt>
attribute. For example, the following two statements create identical
<a title="type" class="reference internal" href="#type"><tt class="xref docutils literal">type</tt></a> objects:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; class X(object):
... a = 1
...
&gt;&gt;&gt; X = type(&#39;X&#39;, (object,), dict(a=1))
</pre></div>
</div>

New in version 2.2.
</dd></dl>

<dl class="function">
<dt id="unichr">
<tt class="descname">unichr</tt><big>(</big>i<big>)</big><a class="headerlink" href="#unichr" title="Permalink to this definition">¶</a></dt>
<dd>Return the Unicode string of one character whose Unicode code is the integer
i. For example, <tt class="docutils literal">unichr(97)</tt> returns the string <tt class="docutils literal">u'a'</tt>. This is the
inverse of <a title="ord" class="reference internal" href="#ord"><tt class="xref docutils literal">ord()</tt></a> for Unicode strings. The valid range for the argument
depends how Python was configured &#8211; it may be either UCS2 [0..0xFFFF] or UCS4
[0..0x10FFFF]. <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal">ValueError</tt></a> is raised otherwise. For ASCII and 8-bit
strings see <a title="chr" class="reference internal" href="#chr"><tt class="xref docutils literal">chr()</tt></a>.

New in version 2.0.
</dd></dl>

<dl class="function">
<dt id="unicode">
<tt class="descname">unicode</tt><big>(</big>[object[, encoding[, errors]]]<big>)</big><a class="headerlink" href="#unicode" title="Permalink to this definition">¶</a></dt>
<dd>Return the Unicode string version of object using one of the following modes:
If encoding and/or errors are given, <tt class="docutils literal">unicode()</tt> will decode the object
which can either be an 8-bit string or a character buffer using the codec for
encoding. The encoding parameter is a string giving the name of an encoding;
if the encoding is not known, <a title="exceptions.LookupError" class="reference external" href="exceptions.html#exceptions.LookupError"><tt class="xref docutils literal">LookupError</tt></a> is raised. Error handling is
done according to errors; this specifies the treatment of characters which are
invalid in the input encoding. If errors is <tt class="docutils literal">'strict'</tt> (the default), a
<a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal">ValueError</tt></a> is raised on errors, while a value of <tt class="docutils literal">'ignore'</tt> causes
errors to be silently ignored, and a value of <tt class="docutils literal">'replace'</tt> causes the official
Unicode replacement character, <tt class="docutils literal">U+FFFD</tt>, to be used to replace input
characters which cannot be decoded. See also the <a title="Encode and decode data and streams." class="reference external" href="codecs.html#module-codecs"><tt class="xref docutils literal">codecs</tt></a> module.
If no optional parameters are given, <tt class="docutils literal">unicode()</tt> will mimic the behaviour of
<tt class="docutils literal">str()</tt> except that it returns Unicode strings instead of 8-bit strings. More
precisely, if object is a Unicode string or subclass it will return that
Unicode string without any additional decoding applied.
For objects which provide a <a title="object.__unicode__" class="reference external" href="../reference/datamodel.html#object.__unicode__"><tt class="xref docutils literal">__unicode__()</tt></a> method, it will call this method
without arguments to create a Unicode string. For all other objects, the 8-bit
string version or representation is requested and then converted to a Unicode
string using the codec for the default encoding in <tt class="docutils literal">'strict'</tt> mode.
For more information on Unicode strings see <a class="reference external" href="stdtypes.html#typesseq">Sequence Types &#8212; str, unicode, list, tuple, buffer, xrange</a> which describes
sequence functionality (Unicode strings are sequences), and also the
string-specific methods described in the <a class="reference external" href="stdtypes.html#string-methods">String Methods</a> section. To
output formatted strings use template strings or the <tt class="docutils literal">%</tt> operator described
in the <a class="reference external" href="stdtypes.html#string-formatting">String Formatting Operations</a> section. In addition see the
<a class="reference external" href="strings.html#stringservices">String Services</a> section. See also <a title="str" class="reference internal" href="#str"><tt class="xref docutils literal">str()</tt></a>.

New in version 2.0.

Changed in version 2.2: Support for <a title="object.__unicode__" class="reference external" href="../reference/datamodel.html#object.__unicode__"><tt class="xref docutils literal">__unicode__()</tt></a> added.
</dd></dl>

<dl class="function">
<dt id="vars">
<tt class="descname">vars</tt><big>(</big>[object]<big>)</big><a class="headerlink" href="#vars" title="Permalink to this definition">¶</a></dt>
<dd>Without an argument, act like <a title="locals" class="reference internal" href="#locals"><tt class="xref docutils literal">locals()</tt></a>.
With a module, class or class instance object as argument (or anything else that
has a <tt class="xref docutils literal">__dict__</tt> attribute), return that attribute.
<div class="admonition note">
Note
The returned dictionary should not be modified:
the effects on the corresponding symbol table are undefined. <a class="footnote-reference" href="#id6" id="id3">[3]</a>
</div>
</dd></dl>

<dl class="function">
<dt id="xrange">
<tt class="descname">xrange</tt><big>(</big>[start], stop[, step]<big>)</big><a class="headerlink" href="#xrange" title="Permalink to this definition">¶</a></dt>
<dd>This function is very similar to <a title="range" class="reference internal" href="#range"><tt class="xref docutils literal">range()</tt></a>, but returns an &#8220;xrange object&#8221;
instead of a list. This is an opaque sequence type which yields the same values
as the corresponding list, without actually storing them all simultaneously.
The advantage of <a title="xrange" class="reference internal" href="#xrange"><tt class="xref docutils literal">xrange()</tt></a> over <a title="range" class="reference internal" href="#range"><tt class="xref docutils literal">range()</tt></a> is minimal (since
<a title="xrange" class="reference internal" href="#xrange"><tt class="xref docutils literal">xrange()</tt></a> still has to create the values when asked for them) except when a
very large range is used on a memory-starved machine or when all of the range&#8217;s
elements are never used (such as when the loop is usually terminated with
<a class="reference external" href="../reference/simple_stmts.html#break"><tt class="xref docutils literal">break</tt></a>).
<div class="impl-detail compound">
CPython implementation detail: <a title="xrange" class="reference internal" href="#xrange"><tt class="xref docutils literal">xrange()</tt></a> is intended to be simple and fast. Implementations may
impose restrictions to achieve this. The C implementation of Python
restricts all arguments to native C longs (&#8220;short&#8221; Python integers), and
also requires that the number of elements fit in a native C long. If a
larger range is needed, an alternate version can be crafted using the
<a title="Functions creating iterators for efficient looping." class="reference external" href="itertools.html#module-itertools"><tt class="xref docutils literal">itertools</tt></a> module: <tt class="docutils literal">takewhile(lambda x: x&lt;stop, (start+i*step
for i in count()))</tt>.
</div>
</dd></dl>

<dl class="function">
<dt id="zip">
<tt class="descname">zip</tt><big>(</big>[iterable, ...]<big>)</big><a class="headerlink" href="#zip" title="Permalink to this definition">¶</a></dt>
<dd>This function returns a list of tuples, where the i-th tuple contains the
i-th element from each of the argument sequences or iterables. The returned
list is truncated in length to the length of the shortest argument sequence.
When there are multiple arguments which are all of the same length, <a title="zip" class="reference internal" href="#zip"><tt class="xref docutils literal">zip()</tt></a>
is similar to <a title="map" class="reference internal" href="#map"><tt class="xref docutils literal">map()</tt></a> with an initial argument of <tt class="xref docutils literal">None</tt>. With a single
sequence argument, it returns a list of 1-tuples. With no arguments, it returns
an empty list.
The left-to-right evaluation order of the iterables is guaranteed. This
makes possible an idiom for clustering a data series into n-length groups
using <tt class="docutils literal">zip(*[iter(s)]*n)</tt>.
<a title="zip" class="reference internal" href="#zip"><tt class="xref docutils literal">zip()</tt></a> in conjunction with the <tt class="docutils literal">*</tt> operator can be used to unzip a
list:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; x = [1, 2, 3]
&gt;&gt;&gt; y = [4, 5, 6]
&gt;&gt;&gt; zipped = zip(x, y)
&gt;&gt;&gt; zipped
[(1, 4), (2, 5), (3, 6)]
&gt;&gt;&gt; x2, y2 = zip(*zipped)
&gt;&gt;&gt; x == list(x2) and y == list(y2)
True
</pre></div>
</div>

New in version 2.0.

Changed in version 2.4: Formerly, <a title="zip" class="reference internal" href="#zip"><tt class="xref docutils literal">zip()</tt></a> required at least one argument and <tt class="docutils literal">zip()</tt> raised a
<a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a> instead of returning an empty list.
</dd></dl>

<dl class="function">
<dt id="__import__">
<tt class="descname">__import__</tt><big>(</big>name[, globals[, locals[, fromlist[, level]]]]<big>)</big><a class="headerlink" href="#__import__" title="Permalink to this definition">¶</a></dt>
<dd><div class="admonition note" id="index-351">
Note
This is an advanced function that is not needed in everyday Python
programming.
</div>
This function is invoked by the <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement. It can be
replaced (by importing the <a title="The module that provides the built-in namespace." class="reference external" href="__builtin__.html#module-__builtin__"><tt class="xref docutils literal">__builtin__</tt></a> module and assigning to
<tt class="docutils literal">__builtin__.__import__</tt>) in order to change semantics of the
<a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement, but nowadays it is usually simpler to use import
hooks (see <a class="reference external" href="http://www.python.org/dev/peps/pep-0302">PEP 302</a>). Direct use of <a title="__import__" class="reference internal" href="#__import__"><tt class="xref docutils literal">__import__()</tt></a> is rare, except in
cases where you want to import a module whose name is only known at runtime.
The function imports the module name, potentially using the given globals
and locals to determine how to interpret the name in a package context.
The fromlist gives the names of objects or submodules that should be
imported from the module given by name. The standard implementation does
not use its locals argument at all, and uses its globals only to
determine the package context of the <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement.
level specifies whether to use absolute or relative imports. The default
is <tt class="docutils literal">-1</tt> which indicates both absolute and relative imports will be
attempted. <tt class="docutils literal">0</tt> means only perform absolute imports. Positive values for
level indicate the number of parent directories to search relative to the
directory of the module calling <a title="__import__" class="reference internal" href="#__import__"><tt class="xref docutils literal">__import__()</tt></a>.
When the name variable is of the form <tt class="docutils literal">package.module</tt>, normally, the
top-level package (the name up till the first dot) is returned, not the
module named by name. However, when a non-empty fromlist argument is
given, the module named by name is returned.
For example, the statement <tt class="docutils literal">import spam</tt> results in bytecode resembling the
following code:
<div class="highlight-python"><div class="highlight"><pre>spam = __import__(&#39;spam&#39;, globals(), locals(), [], -1)
</pre></div>
</div>
The statement <tt class="docutils literal">import spam.ham</tt> results in this call:
<div class="highlight-python"><div class="highlight"><pre>spam = __import__(&#39;spam.ham&#39;, globals(), locals(), [], -1)
</pre></div>
</div>
Note how <a title="__import__" class="reference internal" href="#__import__"><tt class="xref docutils literal">__import__()</tt></a> returns the toplevel module here because this is
the object that is bound to a name by the <a class="reference external" href="../reference/simple_stmts.html#import"><tt class="xref docutils literal">import</tt></a> statement.
On the other hand, the statement <tt class="docutils literal">from spam.ham import eggs, sausage as
saus</tt> results in
<div class="highlight-python"><div class="highlight"><pre>_temp = __import__(&#39;spam.ham&#39;, globals(), locals(), [&#39;eggs&#39;, &#39;sausage&#39;], -1)
eggs = _temp.eggs
saus = _temp.sausage
</pre></div>
</div>
Here, the <tt class="docutils literal">spam.ham</tt> module is returned from <a title="__import__" class="reference internal" href="#__import__"><tt class="xref docutils literal">__import__()</tt></a>. From this
object, the names to import are retrieved and assigned to their respective
names.
If you simply want to import a module (potentially within a package) by name,
you can call <a title="__import__" class="reference internal" href="#__import__"><tt class="xref docutils literal">__import__()</tt></a> and then look it up in <a title="sys.modules" class="reference external" href="sys.html#sys.modules"><tt class="xref docutils literal">sys.modules</tt></a>:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import sys
&gt;&gt;&gt; name = &#39;foo.bar.baz&#39;
&gt;&gt;&gt; __import__(name)
&lt;module &#39;foo&#39; from ...&gt;
&gt;&gt;&gt; baz = sys.modules[name]
&gt;&gt;&gt; baz
&lt;module &#39;foo.bar.baz&#39; from ...&gt;
</pre></div>
</div>

Changed in version 2.5: The level parameter was added.

Changed in version 2.5: Keyword support for parameters was added.
</dd></dl>

</div>
<div class="section" id="non-essential-built-in-functions">
<h1>3. Non-essential Built-in Functions<a class="headerlink" href="#non-essential-built-in-functions" title="Permalink to this headline">¶</a></h1>
There are several built-in functions that are no longer essential to learn, know
or use in modern Python programming. They have been kept here to maintain
backwards compatibility with programs written for older versions of Python.
Python programmers, trainers, students and book writers should feel free to
bypass these functions without concerns about missing something important.
<dl class="function">
<dt id="apply">
<tt class="descname">apply</tt><big>(</big>function, args[, keywords]<big>)</big><a class="headerlink" href="#apply" title="Permalink to this definition">¶</a></dt>
<dd>The function argument must be a callable object (a user-defined or built-in
function or method, or a class object) and the args argument must be a
sequence. The function is called with args as the argument list; the number
of arguments is the length of the tuple. If the optional keywords argument is
present, it must be a dictionary whose keys are strings. It specifies keyword
arguments to be added to the end of the argument list. Calling <a title="apply" class="reference internal" href="#apply"><tt class="xref docutils literal">apply()</tt></a> is
different from just calling <tt class="docutils literal">function(args)</tt>, since in that case there is
always exactly one argument. The use of <a title="apply" class="reference internal" href="#apply"><tt class="xref docutils literal">apply()</tt></a> is equivalent to
<tt class="docutils literal">function(*args, **keywords)</tt>.

Deprecated since version 2.3: Use the extended call syntax with <tt class="docutils literal">*args</tt> and <tt class="docutils literal">**keywords</tt> instead.
</dd></dl>

<dl class="function">
<dt id="buffer">
<tt class="descname">buffer</tt><big>(</big>object[, offset[, size]]<big>)</big><a class="headerlink" href="#buffer" title="Permalink to this definition">¶</a></dt>
<dd>The object argument must be an object that supports the buffer call interface
(such as strings, arrays, and buffers). A new buffer object will be created
which references the object argument. The buffer object will be a slice from
the beginning of object (or from the specified offset). The slice will
extend to the end of object (or will have a length given by the size
argument).</dd></dl>

<dl class="function">
<dt id="coerce">
<tt class="descname">coerce</tt><big>(</big>x, y<big>)</big><a class="headerlink" href="#coerce" title="Permalink to this definition">¶</a></dt>
<dd>Return a tuple consisting of the two numeric arguments converted to a common
type, using the same rules as used by arithmetic operations. If coercion is not
possible, raise <a title="exceptions.TypeError" class="reference external" href="exceptions.html#exceptions.TypeError"><tt class="xref docutils literal">TypeError</tt></a>.</dd></dl>

<dl class="function">
<dt id="intern">
<tt class="descname">intern</tt><big>(</big>string<big>)</big><a class="headerlink" href="#intern" title="Permalink to this definition">¶</a></dt>
<dd>Enter string in the table of &#8220;interned&#8221; strings and return the interned string
&#8211; which is string itself or a copy. Interning strings is useful to gain a
little performance on dictionary lookup &#8211; if the keys in a dictionary are
interned, and the lookup key is interned, the key comparisons (after hashing)
can be done by a pointer compare instead of a string compare. Normally, the
names used in Python programs are automatically interned, and the dictionaries
used to hold module, class or instance attributes have interned keys.

Changed in version 2.3: Interned strings are not immortal (like they used to be in Python 2.2 and
before); you must keep a reference to the return value of <a title="intern" class="reference internal" href="#intern"><tt class="xref docutils literal">intern()</tt></a> around
to benefit from it.
</dd></dl>

Footnotes
<table class="docutils footnote" frame="void" id="id4" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>It is used relatively rarely so does not warrant being made into a statement.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id5" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id2">[2]</a></td><td>Specifying a buffer size currently has no effect on systems that don&#8217;t have
<tt class="xref docutils literal">setvbuf()</tt>. The interface to specify the buffer size is not done using a
method that calls <tt class="xref docutils literal">setvbuf()</tt>, because that may dump core when called after
any I/O has been performed, and there&#8217;s no reliable way to determine whether
this is the case.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id6" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id3">[3]</a></td><td>In the current implementation, local variable bindings cannot normally be
affected this way, but variables retrieved from other scopes (such as modules)
can be. This may change.</td></tr>
</tbody>
</table>
</div>

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<li><a class="reference external" href="#">2. Built-in Functions</a></li>
<li><a class="reference external" href="#non-essential-built-in-functions">3. Non-essential Built-in Functions</a></li>
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