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 <div class="section" id="module-urllib">
<h1>20.5. <tt class="xref docutils literal">urllib</tt> &#8212; Open arbitrary resources by URL<a class="headerlink" href="#module-urllib" title="Permalink to this headline">¶</a></h1>
<div class="admonition note">
Note
The <tt class="xref docutils literal">urllib</tt> module has been split into parts and renamed in
Python 3.0 to <tt class="xref docutils literal">urllib.request</tt>, <tt class="xref docutils literal">urllib.parse</tt>,
and <tt class="xref docutils literal">urllib.error</tt>. The <a class="reference external" href="../glossary.html#term-to3">2to3</a> tool will automatically adapt
imports when converting your sources to 3.0.
Also note that the <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urllib.urlopen()</tt></a> function has been removed in
Python 3.0 in favor of <a title="urllib2.urlopen" class="reference external" href="urllib2.html#urllib2.urlopen"><tt class="xref docutils literal">urllib2.urlopen()</tt></a>.
</div>
This module provides a high-level interface for fetching data across the World
Wide Web. In particular, the <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> function is similar to the
built-in function <a title="open" class="reference external" href="functions.html#open"><tt class="xref docutils literal">open()</tt></a>, but accepts Universal Resource Locators (URLs)
instead of filenames. Some restrictions apply &#8212; it can only open URLs for
reading, and no seek operations are available.
<div class="section" id="high-level-interface">
<h2>20.5.1. High-level interface<a class="headerlink" href="#high-level-interface" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="urllib.urlopen">
<tt class="descclassname">urllib.</tt><tt class="descname">urlopen</tt><big>(</big>url[, data[, proxies]]<big>)</big><a class="headerlink" href="#urllib.urlopen" title="Permalink to this definition">¶</a></dt>
<dd>Open a network object denoted by a URL for reading. If the URL does not have a
scheme identifier, or if it has <tt class="docutils literal">file:</tt> as its scheme identifier, this
opens a local file (without universal newlines); otherwise it opens a socket to
a server somewhere on the network. If the connection cannot be made the
<a title="exceptions.IOError" class="reference external" href="exceptions.html#exceptions.IOError"><tt class="xref docutils literal">IOError</tt></a> exception is raised. If all went well, a file-like object is
returned. This supports the following methods: <tt class="xref docutils literal">read()</tt>, <tt class="xref docutils literal">readline()</tt>,
<tt class="xref docutils literal">readlines()</tt>, <tt class="xref docutils literal">fileno()</tt>, <tt class="xref docutils literal">close()</tt>, <tt class="xref docutils literal">info()</tt>, <tt class="xref docutils literal">getcode()</tt> and
<tt class="xref docutils literal">geturl()</tt>. It also has proper support for the <a class="reference external" href="../glossary.html#term-iterator">iterator</a> protocol. One
caveat: the <tt class="xref docutils literal">read()</tt> method, if the size argument is omitted or negative,
may not read until the end of the data stream; there is no good way to determine
that the entire stream from a socket has been read in the general case.
Except for the <tt class="xref docutils literal">info()</tt>, <tt class="xref docutils literal">getcode()</tt> and <tt class="xref docutils literal">geturl()</tt> methods,
these methods have the same interface as for file objects &#8212; see section
<a class="reference external" href="stdtypes.html#bltin-file-objects">File Objects</a> in this manual. (It is not a built-in file object,
however, so it can&#8217;t be used at those few places where a true built-in file
object is required.)
The <tt class="xref docutils literal">info()</tt> method returns an instance of the class
<a title="mimetools.Message" class="reference external" href="mimetools.html#mimetools.Message"><tt class="xref docutils literal">mimetools.Message</tt></a> containing meta-information associated with the
URL. When the method is HTTP, these headers are those returned by the server
at the head of the retrieved HTML page (including Content-Length and
Content-Type). When the method is FTP, a Content-Length header will be
present if (as is now usual) the server passed back a file length in response
to the FTP retrieval request. A Content-Type header will be present if the
MIME type can be guessed. When the method is local-file, returned headers
will include a Date representing the file&#8217;s last-modified time, a
Content-Length giving file size, and a Content-Type containing a guess at the
file&#8217;s type. See also the description of the <a title="Tools for parsing MIME-style message bodies. (deprecated)" class="reference external" href="mimetools.html#module-mimetools"><tt class="xref docutils literal">mimetools</tt></a> module.
The <tt class="xref docutils literal">geturl()</tt> method returns the real URL of the page. In some cases, the
HTTP server redirects a client to another URL. The <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> function
handles this transparently, but in some cases the caller needs to know which URL
the client was redirected to. The <tt class="xref docutils literal">geturl()</tt> method can be used to get at
this redirected URL.
The <tt class="xref docutils literal">getcode()</tt> method returns the HTTP status code that was sent with the
response, or <tt class="xref docutils literal">None</tt> if the URL is no HTTP URL.
If the url uses the <tt class="docutils literal">http:</tt> scheme identifier, the optional data
argument may be given to specify a <tt class="docutils literal">POST</tt> request (normally the request type
is <tt class="docutils literal">GET</tt>). The data argument must be in standard
application/x-www-form-urlencoded format; see the <a title="urllib.urlencode" class="reference internal" href="#urllib.urlencode"><tt class="xref docutils literal">urlencode()</tt></a>
function below.
The <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> function works transparently with proxies which do not
require authentication. In a Unix or Windows environment, set the
http_proxy, or ftp_proxy environment variables to a URL that
identifies the proxy server before starting the Python interpreter. For example
(the <tt class="docutils literal">'%'</tt> is the command prompt):
<div class="highlight-python"><pre>% http_proxy="http://www.someproxy.com:3128"
% export http_proxy
% python
...</pre>
</div>
The no_proxy environment variable can be used to specify hosts which
shouldn&#8217;t be reached via proxy; if set, it should be a comma-separated list
of hostname suffixes, optionally with <tt class="docutils literal">:port</tt> appended, for example
<tt class="docutils literal">cern.ch,ncsa.uiuc.edu,some.host:8080</tt>.
In a Windows environment, if no proxy environment variables are set, proxy
settings are obtained from the registry&#8217;s Internet Settings section.
In a Mac OS X environment, <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> will retrieve proxy information
from the OS X System Configuration Framework, which can be managed with
Network System Preferences panel.
Alternatively, the optional proxies argument may be used to explicitly specify
proxies. It must be a dictionary mapping scheme names to proxy URLs, where an
empty dictionary causes no proxies to be used, and <tt class="xref docutils literal">None</tt> (the default value)
causes environmental proxy settings to be used as discussed above. For
example:
<div class="highlight-python"><div class="highlight"><pre># Use http://www.someproxy.com:3128 for http proxying
proxies = {&#39;http&#39;: &#39;http://www.someproxy.com:3128&#39;}
filehandle = urllib.urlopen(some_url, proxies=proxies)
# Don&#39;t use any proxies
filehandle = urllib.urlopen(some_url, proxies={})
# Use proxies from environment - both versions are equivalent
filehandle = urllib.urlopen(some_url, proxies=None)
filehandle = urllib.urlopen(some_url)
</pre></div>
</div>
Proxies which require authentication for use are not currently supported; this
is considered an implementation limitation.

Changed in version 2.3: Added the proxies support.

Changed in version 2.6: Added <tt class="xref docutils literal">getcode()</tt> to returned object and support for the
no_proxy environment variable.

Deprecated since version 2.6: The <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> function has been removed in Python 3.0 in favor
of <a title="urllib2.urlopen" class="reference external" href="urllib2.html#urllib2.urlopen"><tt class="xref docutils literal">urllib2.urlopen()</tt></a>.
</dd></dl>

<dl class="function">
<dt id="urllib.urlretrieve">
<tt class="descclassname">urllib.</tt><tt class="descname">urlretrieve</tt><big>(</big>url[, filename[, reporthook[, data]]]<big>)</big><a class="headerlink" href="#urllib.urlretrieve" title="Permalink to this definition">¶</a></dt>
<dd>Copy a network object denoted by a URL to a local file, if necessary. If the URL
points to a local file, or a valid cached copy of the object exists, the object
is not copied. Return a tuple <tt class="docutils literal">(filename, headers)</tt> where filename is the
local file name under which the object can be found, and headers is whatever
the <tt class="xref docutils literal">info()</tt> method of the object returned by <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> returned (for
a remote object, possibly cached). Exceptions are the same as for
<a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a>.
The second argument, if present, specifies the file location to copy to (if
absent, the location will be a tempfile with a generated name). The third
argument, if present, is a hook function that will be called once on
establishment of the network connection and once after each block read
thereafter. The hook will be passed three arguments; a count of blocks
transferred so far, a block size in bytes, and the total size of the file. The
third argument may be <tt class="docutils literal">-1</tt> on older FTP servers which do not return a file
size in response to a retrieval request.
If the url uses the <tt class="docutils literal">http:</tt> scheme identifier, the optional data
argument may be given to specify a <tt class="docutils literal">POST</tt> request (normally the request type
is <tt class="docutils literal">GET</tt>). The data argument must in standard
application/x-www-form-urlencoded format; see the <a title="urllib.urlencode" class="reference internal" href="#urllib.urlencode"><tt class="xref docutils literal">urlencode()</tt></a>
function below.

Changed in version 2.5: <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> will raise <a title="urllib.ContentTooShortError" class="reference internal" href="#urllib.ContentTooShortError"><tt class="xref docutils literal">ContentTooShortError</tt></a> when it detects that
the amount of data available was less than the expected amount (which is the
size reported by a Content-Length header). This can occur, for example, when
the download is interrupted.The Content-Length is treated as a lower bound: if there&#8217;s more data to read,
urlretrieve reads more data, but if less data is available, it raises the
exception.
You can still retrieve the downloaded data in this case, it is stored in the
<tt class="xref docutils literal">content</tt> attribute of the exception instance.
If no Content-Length header was supplied, urlretrieve can not check the size
of the data it has downloaded, and just returns it. In this case you just have
to assume that the download was successful.

</dd></dl>

<dl class="data">
<dt id="urllib._urlopener">
<tt class="descclassname">urllib.</tt><tt class="descname">_urlopener</tt><a class="headerlink" href="#urllib._urlopener" title="Permalink to this definition">¶</a></dt>
<dd>The public functions <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> and <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> create an instance
of the <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a> class and use it to perform their requested
actions. To override this functionality, programmers can create a subclass of
<a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> or <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a>, then assign an instance of that
class to the <tt class="docutils literal">urllib._urlopener</tt> variable before calling the desired function.
For example, applications may want to specify a different
User-Agent header than <a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> defines. This can be
accomplished with the following code:
<div class="highlight-python"><div class="highlight"><pre>import urllib

class AppURLopener(urllib.FancyURLopener):
 version = &quot;App/1.7&quot;

urllib._urlopener = AppURLopener()
</pre></div>
</div>
</dd></dl>

<dl class="function">
<dt id="urllib.urlcleanup">
<tt class="descclassname">urllib.</tt><tt class="descname">urlcleanup</tt><big>(</big><big>)</big><a class="headerlink" href="#urllib.urlcleanup" title="Permalink to this definition">¶</a></dt>
<dd>Clear the cache that may have been built up by previous calls to
<a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a>.</dd></dl>

</div>
<div class="section" id="utility-functions">
<h2>20.5.2. Utility functions<a class="headerlink" href="#utility-functions" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="urllib.quote">
<tt class="descclassname">urllib.</tt><tt class="descname">quote</tt><big>(</big>string[, safe]<big>)</big><a class="headerlink" href="#urllib.quote" title="Permalink to this definition">¶</a></dt>
<dd>Replace special characters in string using the <tt class="docutils literal">%xx</tt> escape. Letters,
digits, and the characters <tt class="docutils literal">'_.-'</tt> are never quoted. By default, this
function is intended for quoting the path section of the URL.The optional
safe parameter specifies additional characters that should not be quoted
&#8212; its default value is <tt class="docutils literal">'/'</tt>.
Example: <tt class="docutils literal">quote('/~connolly/')</tt> yields <tt class="docutils literal">'/%7econnolly/'</tt>.
</dd></dl>

<dl class="function">
<dt id="urllib.quote_plus">
<tt class="descclassname">urllib.</tt><tt class="descname">quote_plus</tt><big>(</big>string[, safe]<big>)</big><a class="headerlink" href="#urllib.quote_plus" title="Permalink to this definition">¶</a></dt>
<dd>Like <a title="urllib.quote" class="reference internal" href="#urllib.quote"><tt class="xref docutils literal">quote()</tt></a>, but also replaces spaces by plus signs, as required for
quoting HTML form values when building up a query string to go into a URL.
Plus signs in the original string are escaped unless they are included in
safe. It also does not have safe default to <tt class="docutils literal">'/'</tt>.</dd></dl>

<dl class="function">
<dt id="urllib.unquote">
<tt class="descclassname">urllib.</tt><tt class="descname">unquote</tt><big>(</big>string<big>)</big><a class="headerlink" href="#urllib.unquote" title="Permalink to this definition">¶</a></dt>
<dd>Replace <tt class="docutils literal">%xx</tt> escapes by their single-character equivalent.
Example: <tt class="docutils literal">unquote('/%7Econnolly/')</tt> yields <tt class="docutils literal">'/~connolly/'</tt>.
</dd></dl>

<dl class="function">
<dt id="urllib.unquote_plus">
<tt class="descclassname">urllib.</tt><tt class="descname">unquote_plus</tt><big>(</big>string<big>)</big><a class="headerlink" href="#urllib.unquote_plus" title="Permalink to this definition">¶</a></dt>
<dd>Like <a title="urllib.unquote" class="reference internal" href="#urllib.unquote"><tt class="xref docutils literal">unquote()</tt></a>, but also replaces plus signs by spaces, as required for
unquoting HTML form values.</dd></dl>

<dl class="function">
<dt id="urllib.urlencode">
<tt class="descclassname">urllib.</tt><tt class="descname">urlencode</tt><big>(</big>query[, doseq]<big>)</big><a class="headerlink" href="#urllib.urlencode" title="Permalink to this definition">¶</a></dt>
<dd>Convert a mapping object or a sequence of two-element tuples to a
&#8220;url-encoded&#8221; string, suitable to pass to <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> above as the
optional data argument. This is useful to pass a dictionary of form
fields to a <tt class="docutils literal">POST</tt> request. The resulting string is a series of
<tt class="docutils literal">key=value</tt> pairs separated by <tt class="docutils literal">'&amp;'</tt> characters, where both key and
value are quoted using <a title="urllib.quote_plus" class="reference internal" href="#urllib.quote_plus"><tt class="xref docutils literal">quote_plus()</tt></a> above. When a sequence of
two-element tuples is used as the query argument, the first element of
each tuple is a key and the second is a value. The value element in itself
can be a sequence and in that case, if the optional parameter doseq is
evaluates to True, individual <tt class="docutils literal">key=value</tt> pairs separated by <tt class="docutils literal">'&amp;'</tt> are
generated for each element of the value sequence for the key. The order of
parameters in the encoded string will match the order of parameter tuples in
the sequence. The <a title="Parse URLs into or assemble them from components." class="reference external" href="urlparse.html#module-urlparse"><tt class="xref docutils literal">urlparse</tt></a> module provides the functions
<tt class="xref docutils literal">parse_qs()</tt> and <tt class="xref docutils literal">parse_qsl()</tt> which are used to parse query strings
into Python data structures.</dd></dl>

<dl class="function">
<dt id="urllib.pathname2url">
<tt class="descclassname">urllib.</tt><tt class="descname">pathname2url</tt><big>(</big>path<big>)</big><a class="headerlink" href="#urllib.pathname2url" title="Permalink to this definition">¶</a></dt>
<dd>Convert the pathname path from the local syntax for a path to the form used in
the path component of a URL. This does not produce a complete URL. The return
value will already be quoted using the <a title="urllib.quote" class="reference internal" href="#urllib.quote"><tt class="xref docutils literal">quote()</tt></a> function.</dd></dl>

<dl class="function">
<dt id="urllib.url2pathname">
<tt class="descclassname">urllib.</tt><tt class="descname">url2pathname</tt><big>(</big>path<big>)</big><a class="headerlink" href="#urllib.url2pathname" title="Permalink to this definition">¶</a></dt>
<dd>Convert the path component path from an encoded URL to the local syntax for a
path. This does not accept a complete URL. This function uses <a title="urllib.unquote" class="reference internal" href="#urllib.unquote"><tt class="xref docutils literal">unquote()</tt></a>
to decode path.</dd></dl>

<dl class="function">
<dt id="urllib.getproxies">
<tt class="descclassname">urllib.</tt><tt class="descname">getproxies</tt><big>(</big><big>)</big><a class="headerlink" href="#urllib.getproxies" title="Permalink to this definition">¶</a></dt>
<dd>This helper function returns a dictionary of scheme to proxy server URL
mappings. It scans the environment for variables named <tt class="docutils literal">&lt;scheme&gt;_proxy</tt>
for all operating systems first, and when it cannot find it, looks for proxy
information from Mac OSX System Configuration for Mac OS X and Windows
Systems Registry for Windows.</dd></dl>

</div>
<div class="section" id="url-opener-objects">
<h2>20.5.3. URL Opener objects<a class="headerlink" href="#url-opener-objects" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="urllib.URLopener">
class <tt class="descclassname">urllib.</tt><tt class="descname">URLopener</tt><big>(</big>[proxies[, **x509]]<big>)</big><a class="headerlink" href="#urllib.URLopener" title="Permalink to this definition">¶</a></dt>
<dd>Base class for opening and reading URLs. Unless you need to support opening
objects using schemes other than <tt class="docutils literal">http:</tt>, <tt class="docutils literal">ftp:</tt>, or <tt class="docutils literal">file:</tt>,
you probably want to use <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a>.
By default, the <a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> class sends a User-Agent header
of <tt class="docutils literal">urllib/VVV</tt>, where VVV is the <tt class="xref docutils literal">urllib</tt> version number.
Applications can define their own User-Agent header by subclassing
<a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> or <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a> and setting the class attribute
<a title="urllib.URLopener.version" class="reference internal" href="#urllib.URLopener.version"><tt class="xref docutils literal">version</tt></a> to an appropriate string value in the subclass definition.
The optional proxies parameter should be a dictionary mapping scheme names to
proxy URLs, where an empty dictionary turns proxies off completely. Its default
value is <tt class="xref docutils literal">None</tt>, in which case environmental proxy settings will be used if
present, as discussed in the definition of <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a>, above.
Additional keyword parameters, collected in x509, may be used for
authentication of the client when using the <tt class="docutils literal">https:</tt> scheme. The keywords
key_file and cert_file are supported to provide an SSL key and certificate;
both are needed to support client authentication.
<a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> objects will raise an <a title="exceptions.IOError" class="reference external" href="exceptions.html#exceptions.IOError"><tt class="xref docutils literal">IOError</tt></a> exception if the server
returns an error code.
<blockquote>
<dl class="method">
<dt id="urllib.URLopener.open">
<tt class="descname">open</tt><big>(</big>fullurl[, data]<big>)</big><a class="headerlink" href="#urllib.URLopener.open" title="Permalink to this definition">¶</a></dt>
<dd>Open fullurl using the appropriate protocol. This method sets up cache and
proxy information, then calls the appropriate open method with its input
arguments. If the scheme is not recognized, <a title="urllib.URLopener.open_unknown" class="reference internal" href="#urllib.URLopener.open_unknown"><tt class="xref docutils literal">open_unknown()</tt></a> is called.
The data argument has the same meaning as the data argument of
<a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a>.</dd></dl>

<dl class="method">
<dt id="urllib.URLopener.open_unknown">
<tt class="descname">open_unknown</tt><big>(</big>fullurl[, data]<big>)</big><a class="headerlink" href="#urllib.URLopener.open_unknown" title="Permalink to this definition">¶</a></dt>
<dd>Overridable interface to open unknown URL types.</dd></dl>

<dl class="method">
<dt id="urllib.URLopener.retrieve">
<tt class="descname">retrieve</tt><big>(</big>url[, filename[, reporthook[, data]]]<big>)</big><a class="headerlink" href="#urllib.URLopener.retrieve" title="Permalink to this definition">¶</a></dt>
<dd>Retrieves the contents of url and places it in filename. The return value
is a tuple consisting of a local filename and either a
<a title="mimetools.Message" class="reference external" href="mimetools.html#mimetools.Message"><tt class="xref docutils literal">mimetools.Message</tt></a> object containing the response headers (for remote
URLs) or <tt class="xref docutils literal">None</tt> (for local URLs). The caller must then open and read the
contents of filename. If filename is not given and the URL refers to a
local file, the input filename is returned. If the URL is non-local and
filename is not given, the filename is the output of <a title="tempfile.mktemp" class="reference external" href="tempfile.html#tempfile.mktemp"><tt class="xref docutils literal">tempfile.mktemp()</tt></a>
with a suffix that matches the suffix of the last path component of the input
URL. If reporthook is given, it must be a function accepting three numeric
parameters. It will be called after each chunk of data is read from the
network. reporthook is ignored for local URLs.
If the url uses the <tt class="docutils literal">http:</tt> scheme identifier, the optional data
argument may be given to specify a <tt class="docutils literal">POST</tt> request (normally the request type
is <tt class="docutils literal">GET</tt>). The data argument must in standard
application/x-www-form-urlencoded format; see the <a title="urllib.urlencode" class="reference internal" href="#urllib.urlencode"><tt class="xref docutils literal">urlencode()</tt></a>
function below.
</dd></dl>

<dl class="attribute">
<dt id="urllib.URLopener.version">
<tt class="descname">version</tt><a class="headerlink" href="#urllib.URLopener.version" title="Permalink to this definition">¶</a></dt>
<dd>Variable that specifies the user agent of the opener object. To get
<tt class="xref docutils literal">urllib</tt> to tell servers that it is a particular user agent, set this in a
subclass as a class variable or in the constructor before calling the base
constructor.</dd></dl>

</blockquote>
</dd></dl>

<dl class="class">
<dt id="urllib.FancyURLopener">
class <tt class="descclassname">urllib.</tt><tt class="descname">FancyURLopener</tt><big>(</big>...<big>)</big><a class="headerlink" href="#urllib.FancyURLopener" title="Permalink to this definition">¶</a></dt>
<dd><a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a> subclasses <a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a> providing default handling
for the following HTTP response codes: 301, 302, 303, 307 and 401. For the 30x
response codes listed above, the Location header is used to fetch
the actual URL. For 401 response codes (authentication required), basic HTTP
authentication is performed. For the 30x response codes, recursion is bounded
by the value of the maxtries attribute, which defaults to 10.
For all other response codes, the method <tt class="xref docutils literal">http_error_default()</tt> is called
which you can override in subclasses to handle the error appropriately.
<div class="admonition note">
Note
According to the letter of <a class="reference external" href="http://tools.ietf.org/html/rfc2616.html">RFC 2616</a>, 301 and 302 responses to POST requests
must not be automatically redirected without confirmation by the user. In
reality, browsers do allow automatic redirection of these responses, changing
the POST to a GET, and <tt class="xref docutils literal">urllib</tt> reproduces this behaviour.
</div>
The parameters to the constructor are the same as those for <a title="urllib.URLopener" class="reference internal" href="#urllib.URLopener"><tt class="xref docutils literal">URLopener</tt></a>.
<div class="admonition note">
Note
<blockquote>
When performing basic authentication, a <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a> instance calls
its <a title="urllib.FancyURLopener.prompt_user_passwd" class="reference internal" href="#urllib.FancyURLopener.prompt_user_passwd"><tt class="xref docutils literal">prompt_user_passwd()</tt></a> method. The default implementation asks the
users for the required information on the controlling terminal. A subclass may
override this method to support more appropriate behavior if needed.</blockquote>
The <a title="urllib.FancyURLopener" class="reference internal" href="#urllib.FancyURLopener"><tt class="xref docutils literal">FancyURLopener</tt></a> class offers one additional method that should be
overloaded to provide the appropriate behavior:
<dl class="last method">
<dt id="urllib.FancyURLopener.prompt_user_passwd">
<tt class="descname">prompt_user_passwd</tt><big>(</big>host, realm<big>)</big><a class="headerlink" href="#urllib.FancyURLopener.prompt_user_passwd" title="Permalink to this definition">¶</a></dt>
<dd>Return information needed to authenticate the user at the given host in the
specified security realm. The return value should be a tuple, <tt class="docutils literal">(user,
password)</tt>, which can be used for basic authentication.
The implementation prompts for this information on the terminal; an application
should override this method to use an appropriate interaction model in the local
environment.
</dd></dl>

</div>
</dd></dl>

<dl class="exception">
<dt id="urllib.ContentTooShortError">
exception <tt class="descclassname">urllib.</tt><tt class="descname">ContentTooShortError</tt><big>(</big>msg[, content]<big>)</big><a class="headerlink" href="#urllib.ContentTooShortError" title="Permalink to this definition">¶</a></dt>
<dd>This exception is raised when the <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> function detects that the
amount of the downloaded data is less than the expected amount (given by the
Content-Length header). The <tt class="xref docutils literal">content</tt> attribute stores the downloaded
(and supposedly truncated) data.

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

</div>
<div class="section" id="urllib-restrictions">
<h2>20.5.4. <tt class="xref docutils literal">urllib</tt> Restrictions<a class="headerlink" href="#urllib-restrictions" title="Permalink to this headline">¶</a></h2>
<blockquote>
</blockquote>
<ul id="index-710">
<li>Currently, only the following protocols are supported: HTTP, (versions 0.9 and
1.0), FTP, and local files.
</li>
<li>The caching feature of <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> has been disabled until I find the
time to hack proper processing of Expiration time headers.
</li>
<li>There should be a function to query whether a particular URL is in the cache.
</li>
<li>For backward compatibility, if a URL appears to point to a local file but the
file can&#8217;t be opened, the URL is re-interpreted using the FTP protocol. This
can sometimes cause confusing error messages.
</li>
<li>The <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> and <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> functions can cause arbitrarily
long delays while waiting for a network connection to be set up. This means
that it is difficult to build an interactive Web client using these functions
without using threads.
</li>
<li id="index-711">The data returned by <a title="urllib.urlopen" class="reference internal" href="#urllib.urlopen"><tt class="xref docutils literal">urlopen()</tt></a> or <a title="urllib.urlretrieve" class="reference internal" href="#urllib.urlretrieve"><tt class="xref docutils literal">urlretrieve()</tt></a> is the raw data
returned by the server. This may be binary data (such as an image), plain text
or (for example) HTML. The HTTP protocol provides type information in the reply
header, which can be inspected by looking at the Content-Type
header. If the returned data is HTML, you can use the module <a title="A parser for HTML documents. (deprecated)" class="reference external" href="htmllib.html#module-htmllib"><tt class="xref docutils literal">htmllib</tt></a> to
parse it.
</li>
<li id="index-712">The code handling the FTP protocol cannot differentiate between a file and a
directory. This can lead to unexpected behavior when attempting to read a URL
that points to a file that is not accessible. If the URL ends in a <tt class="docutils literal">/</tt>, it is
assumed to refer to a directory and will be handled accordingly. But if an
attempt to read a file leads to a 550 error (meaning the URL cannot be found or
is not accessible, often for permission reasons), then the path is treated as a
directory in order to handle the case when a directory is specified by a URL but
the trailing <tt class="docutils literal">/</tt> has been left off. This can cause misleading results when
you try to fetch a file whose read permissions make it inaccessible; the FTP
code will try to read it, fail with a 550 error, and then perform a directory
listing for the unreadable file. If fine-grained control is needed, consider
using the <a title="FTP protocol client (requires sockets)." class="reference external" href="ftplib.html#module-ftplib"><tt class="xref docutils literal">ftplib</tt></a> module, subclassing <tt class="xref docutils literal">FancyURLOpener</tt>, or changing
_urlopener to meet your needs.
</li>
<li>This module does not support the use of proxies which require authentication.
This may be implemented in the future.
</li>
<li id="index-713">Although the <tt class="xref docutils literal">urllib</tt> module contains (undocumented) routines to parse
and unparse URL strings, the recommended interface for URL manipulation is in
module <a title="Parse URLs into or assemble them from components." class="reference external" href="urlparse.html#module-urlparse"><tt class="xref docutils literal">urlparse</tt></a>.
</li>
</ul>
</div>
<div class="section" id="examples">
<h2>20.5.5. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
Here is an example session that uses the <tt class="docutils literal">GET</tt> method to retrieve a URL
containing parameters:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import urllib
&gt;&gt;&gt; params = urllib.urlencode({&#39;spam&#39;: 1, &#39;eggs&#39;: 2, &#39;bacon&#39;: 0})
&gt;&gt;&gt; f = urllib.urlopen(&quot;http://www.musi-cal.com/cgi-bin/query?%s&quot; % params)
&gt;&gt;&gt; print f.read()
</pre></div>
</div>
The following example uses the <tt class="docutils literal">POST</tt> method instead:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import urllib
&gt;&gt;&gt; params = urllib.urlencode({&#39;spam&#39;: 1, &#39;eggs&#39;: 2, &#39;bacon&#39;: 0})
&gt;&gt;&gt; f = urllib.urlopen(&quot;http://www.musi-cal.com/cgi-bin/query&quot;, params)
&gt;&gt;&gt; print f.read()
</pre></div>
</div>
The following example uses an explicitly specified HTTP proxy, overriding
environment settings:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import urllib
&gt;&gt;&gt; proxies = {&#39;http&#39;: &#39;http://proxy.example.com:8080/&#39;}
&gt;&gt;&gt; opener = urllib.FancyURLopener(proxies)
&gt;&gt;&gt; f = opener.open(&quot;http://www.python.org&quot;)
&gt;&gt;&gt; f.read()
</pre></div>
</div>
The following example uses no proxies at all, overriding environment settings:
<div class="highlight-python"><div class="highlight"><pre>&gt;&gt;&gt; import urllib
&gt;&gt;&gt; opener = urllib.FancyURLopener({})
&gt;&gt;&gt; f = opener.open(&quot;http://www.python.org/&quot;)
&gt;&gt;&gt; f.read()
</pre></div>
</div>
</div>
</div>

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 <h3><a href="../contents.html">Table Of Contents</a></h3>
 <ul>
<li><a class="reference external" href="#">20.5. <tt class="docutils literal">urllib</tt> &#8212; Open arbitrary resources by URL</a><ul>
<li><a class="reference external" href="#high-level-interface">20.5.1. High-level interface</a></li>
<li><a class="reference external" href="#utility-functions">20.5.2. Utility functions</a></li>
<li><a class="reference external" href="#url-opener-objects">20.5.3. URL Opener objects</a></li>
<li><a class="reference external" href="#urllib-restrictions">20.5.4. <tt class="docutils literal">urllib</tt> Restrictions</a></li>
<li><a class="reference external" href="#examples">20.5.5. Examples</a></li>
</ul>
</li>
</ul>

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