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<H1><A NAME="SECTION0013300000000000000000">
11.3 <tt class="module">urllib</tt> --
Open arbitrary resources by URL</A>
</H1>
<P>
<P>
<P>
This module provides a high-level interface for fetching data across
the World-Wide Web. In particular, the <tt class="function">urlopen()</tt> function
is similar to the built-in function <tt class="function">open()</tt>, but accepts
Universal Resource Locators (URLs) instead of filenames. Some
restrictions apply -- it can only open URLs for reading, and no seek
operations are available.
<P>
It defines the following public functions:
<P>
<dl><dt><b><a name='l2h-1993'><tt class='function'>urlopen</tt></a></b> (<var>url</var><big>[</big><var>, data</var><big>]</big>)
<dd>
Open a network object denoted by a URL for reading. If the URL does
not have a scheme identifier, or if it has <span class="file">file:</span> as its scheme
identifier, this opens a local file; otherwise it opens a socket to a
server somewhere on the network. If the connection cannot be made, or
if the server returns an error code, the <tt class="exception">IOError</tt> exception
is raised. If all went well, a file-like object is returned. This
supports the following methods: <tt class="method">read()</tt>, <tt class="method">readline()</tt>,
<tt class="method">readlines()</tt>, <tt class="method">fileno()</tt>, <tt class="method">close()</tt>,
<tt class="method">info()</tt> and <tt class="method">geturl()</tt>.
<P>
Except for the <tt class="method">info()</tt> and <tt class="method">geturl()</tt> methods,
these methods have the same interface as for
file objects -- see section <A href="bltin-file-objects.html#bltin-file-objects" tppabs="http://www.python.org/doc/current/lib/bltin-file-objects.html#bltin-file-objects">2.1.7</A> in this
manual. (It is not a built-in file object, however, so it can't be
used at those few places where a true built-in file object is
required.)
<P>
The <tt class="method">info()</tt> method returns an instance of the class
<tt class="class">mimetools.Message</tt> 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. When the method is local-file, returned headers will include
a Date representing the file's last-modified time, a Content-Length
giving file size, and a Content-Type containing a guess at the file's
type. See also the description of the
<tt class='module'><a href="module-mimetools.html" tppabs="http://www.python.org/doc/current/lib/module-mimetools.html">mimetools</a></tt> module.
<P>
The <tt class="method">geturl()</tt> method returns the real URL of the page. In
some cases, the HTTP server redirects a client to another URL. The
<tt class="function">urlopen()</tt> function handles this transparently, but in some
cases the caller needs to know which URL the client was redirected
to. The <tt class="method">geturl()</tt> method can be used to get at this
redirected URL.
<P>
If the <var>url</var> uses the <span class="file">http:</span> scheme identifier, the optional
<var>data</var> argument may be given to specify a <code>POST</code> request
(normally the request type is <code>GET</code>). The <var>data</var> argument
must in standard <span class="file">application/x-www-form-urlencoded</span> format;
see the <tt class="function">urlencode()</tt> function below.
<P>
The <tt class="function">urlopen()</tt> function works transparently with proxies
which do not require authentication. In a Unix or Windows
environment, set the <a class="envvar" name='l2h-2005'>$http_proxy</a>, <a class="envvar" name='l2h-2006'>$ftp_proxy</a> or
<a class="envvar" name='l2h-2007'>$gopher_proxy</a> environment variables to a URL that identifies
the proxy server before starting the Python interpreter. For example
(the "<tt class="character">%</tt>" is the command prompt):
<P>
<dl><dd><pre class="verbatim">
% http_proxy="http://www.someproxy.com:3128"
% export http_proxy
% python
...
</pre></dl>
<P>
In a Macintosh environment, <tt class="function">urlopen()</tt> will retrieve proxy
information from Internet Config.
<P>
Proxies which require authentication for use are not currently
supported; this is considered an implementation limitation.
</dl>
<P>
<dl><dt><b><a name='l2h-1994'><tt class='function'>urlretrieve</tt></a></b> (<var>url</var><big>[</big><var>, filename</var><big>[</big><var>, hook</var><big>]</big><big>]</big>)
<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
<code>(<var>filename</var>, <var>headers</var>)</code> where <var>filename</var> is the
local file name under which the object can be found, and <var>headers</var>
is either <code>None</code> (for a local object) or whatever the
<tt class="method">info()</tt> method of the object returned by <tt class="function">urlopen()</tt>
returned (for a remote object, possibly cached). Exceptions are the
same as for <tt class="function">urlopen()</tt>.
<P>
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 <code>-1</code> on older
FTP servers which do not return a file size in response to a retrieval
request.
<P>
If the <var>url</var> uses the <span class="file">http:</span> scheme identifier, the optional
<var>data</var> argument may be given to specify a <code>POST</code> request
(normally the request type is <code>GET</code>). The <var>data</var> argument
must in standard <span class="file">application/x-www-form-urlencoded</span> format;
see the <tt class="function">urlencode()</tt> function below.
</dl>
<P>
<dl><dt><b><a name='l2h-1995'><tt class='function'>urlcleanup</tt></a></b> ()
<dd>
Clear the cache that may have been built up by previous calls to
<tt class="function">urlretrieve()</tt>.
</dl>
<P>
<dl><dt><b><a name='l2h-1996'><tt class='function'>quote</tt></a></b> (<var>string</var><big>[</big><var>, safe</var><big>]</big>)
<dd>
Replace special characters in <var>string</var> using the "<tt class="samp">%xx</tt>" escape.
Letters, digits, and the characters "<tt class="character">_,.-</tt>" are never quoted.
The optional <var>safe</var> parameter specifies additional characters
that should not be quoted -- its default value is <code>'/'</code>.
<P>
Example: <code>quote('/~connolly/')</code> yields <code>'/%7econnolly/'</code>.
</dl>
<P>
<dl><dt><b><a name='l2h-1997'><tt class='function'>quote_plus</tt></a></b> (<var>string</var><big>[</big><var>, safe</var><big>]</big>)
<dd>
Like <tt class="function">quote()</tt>, but also replaces spaces by plus signs, as
required for quoting HTML form values. Plus signs in the original
string are escaped unless they are included in <var>safe</var>.
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