
``urllib2`` --- extensible library for opening URLs
***************************************************

Note: The ``urllib2`` module has been split across several modules in
  Python 3.0 named ``urllib.request`` and ``urllib.error``. The *2to3*
  tool will automatically adapt imports when converting your sources
  to 3.0.

The ``urllib2`` module defines functions and classes which help in
opening URLs (mostly HTTP) in a complex world --- basic and digest
authentication, redirections, cookies and more.

The ``urllib2`` module defines the following functions:

urllib2.urlopen(url[, data][, timeout])

   Open the URL *url*, which can be either a string or a ``Request``
   object.

   *data* may be a string specifying additional data to send to the
   server, or ``None`` if no such data is needed.  Currently HTTP
   requests are the only ones that use *data*; the HTTP request will
   be a POST instead of a GET when the *data* parameter is provided.
   *data* should be a buffer in the standard *application/x-www-form-
   urlencoded* format.  The ``urllib.urlencode()`` function takes a
   mapping or sequence of 2-tuples and returns a string in this
   format.

   The optional *timeout* parameter specifies a timeout in seconds for
   blocking operations like the connection attempt (if not specified,
   the global default timeout setting will be used).  This actually
   only works for HTTP, HTTPS, FTP and FTPS connections.

   This function returns a file-like object with two additional
   methods:

   * ``geturl()`` --- return the URL of the resource retrieved,
     commonly used to determine if a redirect was followed

   * ``info()`` --- return the meta-information of the page, such as
     headers, in the form of an ``mimetools.Message`` instance (see
     Quick Reference to HTTP Headers)

   Raises ``URLError`` on errors.

   Note that ``None`` may be returned if no handler handles the
   request (though the default installed global ``OpenerDirector``
   uses ``UnknownHandler`` to ensure this never happens).

   In addition, default installed ``ProxyHandler`` makes sure the
   requests are handled through the proxy when they are set.

   Changed in version 2.6: *timeout* was added.

urllib2.install_opener(opener)

   Install an ``OpenerDirector`` instance as the default global
   opener. Installing an opener is only necessary if you want urlopen
   to use that opener; otherwise, simply call
   ``OpenerDirector.open()`` instead of ``urlopen()``. The code does
   not check for a real ``OpenerDirector``, and any class with the
   appropriate interface will work.

urllib2.build_opener([handler, ...])

   Return an ``OpenerDirector`` instance, which chains the handlers in
   the order given. *handler*s can be either instances of
   ``BaseHandler``, or subclasses of ``BaseHandler`` (in which case it
   must be possible to call the constructor without any parameters).
   Instances of the following classes will be in front of the
   *handler*s, unless the *handler*s contain them, instances of them
   or subclasses of them: ``ProxyHandler``, ``UnknownHandler``,
   ``HTTPHandler``, ``HTTPDefaultErrorHandler``,
   ``HTTPRedirectHandler``, ``FTPHandler``, ``FileHandler``,
   ``HTTPErrorProcessor``.

   If the Python installation has SSL support (i.e., if the ``ssl``
   module can be imported), ``HTTPSHandler`` will also be added.

   Beginning in Python 2.3, a ``BaseHandler`` subclass may also change
   its ``handler_order`` member variable to modify its position in the
   handlers list.

The following exceptions are raised as appropriate:

exception exception urllib2.URLError

   The handlers raise this exception (or derived exceptions) when they
   run into a problem.  It is a subclass of ``IOError``.

   reason

      The reason for this error.  It can be a message string or
      another exception instance (``socket.error`` for remote URLs,
      ``OSError`` for local URLs).

exception exception urllib2.HTTPError

   Though being an exception (a subclass of ``URLError``), an
   ``HTTPError`` can also function as a non-exceptional file-like
   return value (the same thing that ``urlopen()`` returns).  This is
   useful when handling exotic HTTP errors, such as requests for
   authentication.

   code

      An HTTP status code as defined in RFC 2616. This numeric value
      corresponds to a value found in the dictionary of codes as found
      in ``BaseHTTPServer.BaseHTTPRequestHandler.responses``.

The following classes are provided:

class class urllib2.Request(url[, data][, headers][, origin_req_host][, unverifiable])

   This class is an abstraction of a URL request.

   *url* should be a string containing a valid URL.

   *data* may be a string specifying additional data to send to the
   server, or ``None`` if no such data is needed.  Currently HTTP
   requests are the only ones that use *data*; the HTTP request will
   be a POST instead of a GET when the *data* parameter is provided.
   *data* should be a buffer in the standard *application/x-www-form-
   urlencoded* format.  The ``urllib.urlencode()`` function takes a
   mapping or sequence of 2-tuples and returns a string in this
   format.

   *headers* should be a dictionary, and will be treated as if
   ``add_header()`` was called with each key and value as arguments.
   This is often used to "spoof" the ``User-Agent`` header, which is
   used by a browser to identify itself -- some HTTP servers only
   allow requests coming from common browsers as opposed to scripts.
   For example, Mozilla Firefox may identify itself as ``"Mozilla/5.0
   (X11; U; Linux i686) Gecko/20071127 Firefox/2.0.0.11"``, while
   ``urllib2``'s default user agent string is ``"Python-urllib/2.6"``
   (on Python 2.6).

   The final two arguments are only of interest for correct handling
   of third-party HTTP cookies:

   *origin_req_host* should be the request-host of the origin
   transaction, as defined by **RFC 2965**.  It defaults to
   ``cookielib.request_host(self)``.  This is the host name or IP
   address of the original request that was initiated by the user.
   For example, if the request is for an image in an HTML document,
   this should be the request-host of the request for the page
   containing the image.

   *unverifiable* should indicate whether the request is unverifiable,
   as defined by RFC 2965.  It defaults to False.  An unverifiable
   request is one whose URL the user did not have the option to
   approve.  For example, if the request is for an image in an HTML
   document, and the user had no option to approve the automatic
   fetching of the image, this should be true.

class class urllib2.OpenerDirector

   The ``OpenerDirector`` class opens URLs via ``BaseHandler``s
   chained together. It manages the chaining of handlers, and recovery
   from errors.

class class urllib2.BaseHandler

   This is the base class for all registered handlers --- and handles
   only the simple mechanics of registration.

class class urllib2.HTTPDefaultErrorHandler

   A class which defines a default handler for HTTP error responses;
   all responses are turned into ``HTTPError`` exceptions.

class class urllib2.HTTPRedirectHandler

   A class to handle redirections.

class class urllib2.HTTPCookieProcessor([cookiejar])

   A class to handle HTTP Cookies.

class class urllib2.ProxyHandler([proxies])

   Cause requests to go through a proxy. If *proxies* is given, it
   must be a dictionary mapping protocol names to URLs of proxies. The
   default is to read the list of proxies from the environment
   variables ****.  If no proxy environment variables are set, in a
   Windows environment, proxy settings are obtained from the
   registry's Internet Settings section and in a Mac OS X
   environment, proxy information is retrieved from the OS X System
   Configuration Framework.

   To disable autodetected proxy pass an empty dictionary.

class class urllib2.HTTPPasswordMgr

   Keep a database of  ``(realm, uri) -> (user, password)`` mappings.

class class urllib2.HTTPPasswordMgrWithDefaultRealm

   Keep a database of  ``(realm, uri) -> (user, password)`` mappings.
   A realm of ``None`` is considered a catch-all realm, which is
   searched if no other realm fits.

class class urllib2.AbstractBasicAuthHandler([password_mgr])

   This is a mixin class that helps with HTTP authentication, both to
   the remote host and to a proxy. *password_mgr*, if given, should be
   something that is compatible with ``HTTPPasswordMgr``; refer to
   section *HTTPPasswordMgr Objects* for information on the interface
   that must be supported.

class class urllib2.HTTPBasicAuthHandler([password_mgr])

   Handle authentication with the remote host. *password_mgr*, if
   given, should be something that is compatible with
   ``HTTPPasswordMgr``; refer to section *HTTPPasswordMgr Objects* for
   information on the interface that must be supported.

class class urllib2.ProxyBasicAuthHandler([password_mgr])

   Handle authentication with the proxy. *password_mgr*, if given,
   should be something that is compatible with ``HTTPPasswordMgr``;
   refer to section *HTTPPasswordMgr Objects* for information on the
   interface that must be supported.

class class urllib2.AbstractDigestAuthHandler([password_mgr])

   This is a mixin class that helps with HTTP authentication, both to
   the remote host and to a proxy. *password_mgr*, if given, should be
   something that is compatible with ``HTTPPasswordMgr``; refer to
   section *HTTPPasswordMgr Objects* for information on the interface
   that must be supported.

class class urllib2.HTTPDigestAuthHandler([password_mgr])

   Handle authentication with the remote host. *password_mgr*, if
   given, should be something that is compatible with
   ``HTTPPasswordMgr``; refer to section *HTTPPasswordMgr Objects* for
   information on the interface that must be supported.

class class urllib2.ProxyDigestAuthHandler([password_mgr])

   Handle authentication with the proxy. *password_mgr*, if given,
   should be something that is compatible with ``HTTPPasswordMgr``;
   refer to section *HTTPPasswordMgr Objects* for information on the
   interface that must be supported.

class class urllib2.HTTPHandler

   A class to handle opening of HTTP URLs.

class class urllib2.HTTPSHandler

   A class to handle opening of HTTPS URLs.

class class urllib2.FileHandler

   Open local files.

class class urllib2.FTPHandler

   Open FTP URLs.

class class urllib2.CacheFTPHandler

   Open FTP URLs, keeping a cache of open FTP connections to minimize
   delays.

class class urllib2.UnknownHandler

   A catch-all class to handle unknown URLs.


Request Objects
===============

The following methods describe all of ``Request``'s public interface,
and so all must be overridden in subclasses.

Request.add_data(data)

   Set the ``Request`` data to *data*.  This is ignored by all
   handlers except HTTP handlers --- and there it should be a byte
   string, and will change the request to be ``POST`` rather than
   ``GET``.

Request.get_method()

   Return a string indicating the HTTP request method.  This is only
   meaningful for HTTP requests, and currently always returns
   ``'GET'`` or ``'POST'``.

Request.has_data()

   Return whether the instance has a non-``None`` data.

Request.get_data()

   Return the instance's data.

Request.add_header(key, val)

   Add another header to the request.  Headers are currently ignored
   by all handlers except HTTP handlers, where they are added to the
   list of headers sent to the server.  Note that there cannot be more
   than one header with the same name, and later calls will overwrite
   previous calls in case the *key* collides. Currently, this is no
   loss of HTTP functionality, since all headers which have meaning
   when used more than once have a (header-specific) way of gaining
   the same functionality using only one header.

Request.add_unredirected_header(key, header)

   Add a header that will not be added to a redirected request.

   New in version 2.4.

Request.has_header(header)

   Return whether the instance has the named header (checks both
   regular and unredirected).

   New in version 2.4.

Request.get_full_url()

   Return the URL given in the constructor.

Request.get_type()

   Return the type of the URL --- also known as the scheme.

Request.get_host()

   Return the host to which a connection will be made.

Request.get_selector()

   Return the selector --- the part of the URL that is sent to the
   server.

Request.set_proxy(host, type)

   Prepare the request by connecting to a proxy server. The *host* and
   *type* will replace those of the instance, and the instance's
   selector will be the original URL given in the constructor.

Request.get_origin_req_host()

   Return the request-host of the origin transaction, as defined by
   **RFC 2965**. See the documentation for the ``Request``
   constructor.

Request.is_unverifiable()

   Return whether the request is unverifiable, as defined by RFC 2965.
   See the documentation for the ``Request`` constructor.


OpenerDirector Objects
======================

``OpenerDirector`` instances have the following methods:

OpenerDirector.add_handler(handler)

   *handler* should be an instance of ``BaseHandler``.  The following
   methods are searched, and added to the possible chains (note that
   HTTP errors are a special case).

   * ``*protocol*_open`` --- signal that the handler knows how to open
     *protocol* URLs.

   * ``http_error_*type*`` --- signal that the handler knows how to
     handle HTTP errors with HTTP error code *type*.

   * ``*protocol*_error`` --- signal that the handler knows how to
     handle errors from (non-``http``) *protocol*.

   * ``*protocol*_request`` --- signal that the handler knows how to
     pre-process *protocol* requests.

   * ``*protocol*_response`` --- signal that the handler knows how to
     post-process *protocol* responses.

OpenerDirector.open(url[, data][, timeout])

   Open the given *url* (which can be a request object or a string),
   optionally passing the given *data*. Arguments, return values and
   exceptions raised are the same as those of ``urlopen()`` (which
   simply calls the ``open()`` method on the currently installed
   global ``OpenerDirector``).  The optional *timeout* parameter
   specifies a timeout in seconds for blocking operations like the
   connection attempt (if not specified, the global default timeout
   setting will be used). The timeout feature actually works only for
   HTTP, HTTPS, FTP and FTPS connections).

   Changed in version 2.6: *timeout* was added.

OpenerDirector.error(proto[, arg[, ...]])

   Handle an error of the given protocol.  This will call the
   registered error handlers for the given protocol with the given
   arguments (which are protocol specific).  The HTTP protocol is a
   special case which uses the HTTP response code to determine the
   specific error handler; refer to the ``http_error_*()`` methods of
   the handler classes.

   Return values and exceptions raised are the same as those of
   ``urlopen()``.

OpenerDirector objects open URLs in three stages:

The order in which these methods are called within each stage is
determined by sorting the handler instances.

1. Every handler with a method named like ``*protocol*_request`` has
   that method called to pre-process the request.

2. Handlers with a method named like ``*protocol*_open`` are called to
   handle the request. This stage ends when a handler either returns a
   non-``None`` value (ie. a response), or raises an exception
   (usually ``URLError``). Exceptions are allowed to propagate.

   In fact, the above algorithm is first tried for methods named
   ``default_open()``.  If all such methods return ``None``, the
   algorithm is repeated for methods named like ``*protocol*_open``.
   If all such methods return ``None``, the algorithm is repeated for
   methods named ``unknown_open()``.

   Note that the implementation of these methods may involve calls of
   the parent ``OpenerDirector`` instance's ``open()`` and ``error()``
   methods.

3. Every handler with a method named like ``*protocol*_response`` has
   that method called to post-process the response.


BaseHandler Objects
===================

``BaseHandler`` objects provide a couple of methods that are directly
useful, and others that are meant to be used by derived classes.
These are intended for direct use:

BaseHandler.add_parent(director)

   Add a director as parent.

BaseHandler.close()

   Remove any parents.

The following members and methods should only be used by classes
derived from ``BaseHandler``.

Note: The convention has been adopted that subclasses defining
  ``protocol_request()`` or ``protocol_response()`` methods are named
  ``*Processor``; all others are named ``*Handler``.

BaseHandler.parent

   A valid ``OpenerDirector``, which can be used to open using a
   different protocol, or handle errors.

BaseHandler.default_open(req)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should define it if they want to catch all URLs.

   This method, if implemented, will be called by the parent
   ``OpenerDirector``.  It should return a file-like object as
   described in the return value of the ``open()`` of
   ``OpenerDirector``, or ``None``. It should raise ``URLError``,
   unless a truly exceptional thing happens (for example,
   ``MemoryError`` should not be mapped to ``URLError``).

   This method will be called before any protocol-specific open
   method.

BaseHandler.protocol_open(req)

   ("protocol" is to be replaced by the protocol name.)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should define it if they want to handle URLs with the given
   *protocol*.

   This method, if defined, will be called by the parent
   ``OpenerDirector``. Return values should be the same as for
   ``default_open()``.

BaseHandler.unknown_open(req)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should define it if they want to catch all URLs with no specific
   registered handler to open it.

   This method, if implemented, will be called by the ``parent``
   ``OpenerDirector``.  Return values should be the same as for
   ``default_open()``.

BaseHandler.http_error_default(req, fp, code, msg, hdrs)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should override it if they intend to provide a catch-all for
   otherwise unhandled HTTP errors.  It will be called automatically
   by the  ``OpenerDirector`` getting the error, and should not
   normally be called in other circumstances.

   *req* will be a ``Request`` object, *fp* will be a file-like object
   with the HTTP error body, *code* will be the three-digit code of
   the error, *msg* will be the user-visible explanation of the code
   and *hdrs* will be a mapping object with the headers of the error.

   Return values and exceptions raised should be the same as those of
   ``urlopen()``.

BaseHandler.http_error_nnn(req, fp, code, msg, hdrs)

   *nnn* should be a three-digit HTTP error code.  This method is also
   not defined in ``BaseHandler``, but will be called, if it exists,
   on an instance of a subclass, when an HTTP error with code *nnn*
   occurs.

   Subclasses should override this method to handle specific HTTP
   errors.

   Arguments, return values and exceptions raised should be the same
   as for ``http_error_default()``.

BaseHandler.protocol_request(req)

   ("protocol" is to be replaced by the protocol name.)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should define it if they want to pre-process requests of the given
   *protocol*.

   This method, if defined, will be called by the parent
   ``OpenerDirector``. *req* will be a ``Request`` object. The return
   value should be a ``Request`` object.

BaseHandler.protocol_response(req, response)

   ("protocol" is to be replaced by the protocol name.)

   This method is *not* defined in ``BaseHandler``, but subclasses
   should define it if they want to post-process responses of the
   given *protocol*.

   This method, if defined, will be called by the parent
   ``OpenerDirector``. *req* will be a ``Request`` object. *response*
   will be an object implementing the same interface as the return
   value of ``urlopen()``.  The return value should implement the same
   interface as the return value of ``urlopen()``.


HTTPRedirectHandler Objects
===========================

Note: Some HTTP redirections require action from this module's client
  code.  If this is the case, ``HTTPError`` is raised.  See **RFC
  2616** for details of the precise meanings of the various
  redirection codes.

HTTPRedirectHandler.redirect_request(req, fp, code, msg, hdrs, newurl)

   Return a ``Request`` or ``None`` in response to a redirect. This is
   called by the default implementations of the ``http_error_30*()``
   methods when a redirection is received from the server.  If a
   redirection should take place, return a new ``Request`` to allow
   ``http_error_30*()`` to perform the redirect to *newurl*.
   Otherwise, raise ``HTTPError`` if no other handler should try to
   handle this URL, or return ``None`` if you can't but another
   handler might.

   Note: The default implementation of this method does not strictly
     follow **RFC 2616**, which says that 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 the default implementation reproduces this behavior.

HTTPRedirectHandler.http_error_301(req, fp, code, msg, hdrs)

   Redirect to the ``Location:`` or ``URI:`` URL.  This method is
   called by the parent ``OpenerDirector`` when getting an HTTP 'moved
   permanently' response.

HTTPRedirectHandler.http_error_302(req, fp, code, msg, hdrs)

   The same as ``http_error_301()``, but called for the 'found'
   response.

HTTPRedirectHandler.http_error_303(req, fp, code, msg, hdrs)

   The same as ``http_error_301()``, but called for the 'see other'
   response.

HTTPRedirectHandler.http_error_307(req, fp, code, msg, hdrs)

   The same as ``http_error_301()``, but called for the 'temporary
   redirect' response.


HTTPCookieProcessor Objects
===========================

New in version 2.4.

``HTTPCookieProcessor`` instances have one attribute:

HTTPCookieProcessor.cookiejar

   The ``cookielib.CookieJar`` in which cookies are stored.


ProxyHandler Objects
====================

ProxyHandler.protocol_open(request)

   ("protocol" is to be replaced by the protocol name.)

   The ``ProxyHandler`` will have a method ``*protocol*_open`` for
   every *protocol* which has a proxy in the *proxies* dictionary
   given in the constructor.  The method will modify requests to go
   through the proxy, by calling ``request.set_proxy()``, and call the
   next handler in the chain to actually execute the protocol.


HTTPPasswordMgr Objects
=======================

These methods are available on ``HTTPPasswordMgr`` and
``HTTPPasswordMgrWithDefaultRealm`` objects.

HTTPPasswordMgr.add_password(realm, uri, user, passwd)

   *uri* can be either a single URI, or a sequence of URIs. *realm*,
   *user* and *passwd* must be strings. This causes ``(user, passwd)``
   to be used as authentication tokens when authentication for *realm*
   and a super-URI of any of the given URIs is given.

HTTPPasswordMgr.find_user_password(realm, authuri)

   Get user/password for given realm and URI, if any.  This method
   will return ``(None, None)`` if there is no matching user/password.

   For ``HTTPPasswordMgrWithDefaultRealm`` objects, the realm ``None``
   will be searched if the given *realm* has no matching
   user/password.


AbstractBasicAuthHandler Objects
================================

AbstractBasicAuthHandler.http_error_auth_reqed(authreq, host, req, headers)

   Handle an authentication request by getting a user/password pair,
   and re-trying the request.  *authreq* should be the name of the
   header where the information about the realm is included in the
   request, *host* specifies the URL and path to authenticate for,
   *req* should be the (failed) ``Request`` object, and *headers*
   should be the error headers.

   *host* is either an authority (e.g. ``"python.org"``) or a URL
   containing an authority component (e.g. ``"http://python.org/"``).
   In either case, the authority must not contain a userinfo component
   (so, ``"python.org"`` and ``"python.org:80"`` are fine,
   ``"joe:password@python.org"`` is not).


HTTPBasicAuthHandler Objects
============================

HTTPBasicAuthHandler.http_error_401(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


ProxyBasicAuthHandler Objects
=============================

ProxyBasicAuthHandler.http_error_407(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


AbstractDigestAuthHandler Objects
=================================

AbstractDigestAuthHandler.http_error_auth_reqed(authreq, host, req, headers)

   *authreq* should be the name of the header where the information
   about the realm is included in the request, *host* should be the
   host to authenticate to, *req* should be the (failed) ``Request``
   object, and *headers* should be the error headers.


HTTPDigestAuthHandler Objects
=============================

HTTPDigestAuthHandler.http_error_401(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


ProxyDigestAuthHandler Objects
==============================

ProxyDigestAuthHandler.http_error_407(req, fp, code, msg, hdrs)

   Retry the request with authentication information, if available.


HTTPHandler Objects
===================

HTTPHandler.http_open(req)

   Send an HTTP request, which can be either GET or POST, depending on
   ``req.has_data()``.


HTTPSHandler Objects
====================

HTTPSHandler.https_open(req)

   Send an HTTPS request, which can be either GET or POST, depending
   on ``req.has_data()``.


FileHandler Objects
===================

FileHandler.file_open(req)

   Open the file locally, if there is no host name, or the host name
   is ``'localhost'``. Change the protocol to ``ftp`` otherwise, and
   retry opening it using ``parent``.


FTPHandler Objects
==================

FTPHandler.ftp_open(req)

   Open the FTP file indicated by *req*. The login is always done with
   empty username and password.


CacheFTPHandler Objects
=======================

``CacheFTPHandler`` objects are ``FTPHandler`` objects with the
following additional methods:

CacheFTPHandler.setTimeout(t)

   Set timeout of connections to *t* seconds.

CacheFTPHandler.setMaxConns(m)

   Set maximum number of cached connections to *m*.


UnknownHandler Objects
======================

UnknownHandler.unknown_open()

   Raise a ``URLError`` exception.


HTTPErrorProcessor Objects
==========================

New in version 2.4.

HTTPErrorProcessor.unknown_open()

   Process HTTP error responses.

   For 200 error codes, the response object is returned immediately.

   For non-200 error codes, this simply passes the job on to the
   ``*protocol*_error_code`` handler methods, via
   ``OpenerDirector.error()``.  Eventually,
   ``urllib2.HTTPDefaultErrorHandler`` will raise an ``HTTPError`` if
   no other handler handles the error.


Examples
========

This example gets the python.org main page and displays the first 100
bytes of it:

   >>> import urllib2
   >>> f = urllib2.urlopen('http://www.python.org/')
   >>> print f.read(100)
   <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
   <?xml-stylesheet href="./css/ht2html

Here we are sending a data-stream to the stdin of a CGI and reading
the data it returns to us. Note that this example will only work when
the Python installation supports SSL.

   >>> import urllib2
   >>> req = urllib2.Request(url='https://localhost/cgi-bin/test.cgi',
   ...                       data='This data is passed to stdin of the CGI')
   >>> f = urllib2.urlopen(req)
   >>> print f.read()
   Got Data: "This data is passed to stdin of the CGI"

The code for the sample CGI used in the above example is:

   #!/usr/bin/env python
   import sys
   data = sys.stdin.read()
   print 'Content-type: text-plain\n\nGot Data: "%s"' % data

Use of Basic HTTP Authentication:

   import urllib2
   # Create an OpenerDirector with support for Basic HTTP Authentication...
   auth_handler = urllib2.HTTPBasicAuthHandler()
   auth_handler.add_password(realm='PDQ Application',
                             uri='https://mahler:8092/site-updates.py',
                             user='klem',
                             passwd='kadidd!ehopper')
   opener = urllib2.build_opener(auth_handler)
   # ...and install it globally so it can be used with urlopen.
   urllib2.install_opener(opener)
   urllib2.urlopen('http://www.example.com/login.html')

``build_opener()`` provides many handlers by default, including a
``ProxyHandler``.  By default, ``ProxyHandler`` uses the environment
variables named ``<scheme>_proxy``, where ``<scheme>`` is the URL
scheme involved.  For example, the **http_proxy** environment variable
is read to obtain the HTTP proxy's URL.

This example replaces the default ``ProxyHandler`` with one that uses
programmatically-supplied proxy URLs, and adds proxy authorization
support with ``ProxyBasicAuthHandler``.

   proxy_handler = urllib2.ProxyHandler({'http': 'http://www.example.com:3128/'})
   proxy_auth_handler = urllib2.ProxyBasicAuthHandler()
   proxy_auth_handler.add_password('realm', 'host', 'username', 'password')

   opener = urllib2.build_opener(proxy_handler, proxy_auth_handler)
   # This time, rather than install the OpenerDirector, we use it directly:
   opener.open('http://www.example.com/login.html')

Adding HTTP headers:

Use the *headers* argument to the ``Request`` constructor, or:

   import urllib2
   req = urllib2.Request('http://www.example.com/')
   req.add_header('Referer', 'http://www.python.org/')
   r = urllib2.urlopen(req)

``OpenerDirector`` automatically adds a *User-Agent* header to every
``Request``.  To change this:

   import urllib2
   opener = urllib2.build_opener()
   opener.addheaders = [('User-agent', 'Mozilla/5.0')]
   opener.open('http://www.example.com/')

Also, remember that a few standard headers (*Content-Length*,
*Content-Type* and *Host*) are added when the ``Request`` is passed to
``urlopen()`` (or ``OpenerDirector.open()``).
