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+
+:mod:`urllib` --- Open arbitrary resources by URL
+=================================================
+
+.. module:: urllib
+   :synopsis: Open an arbitrary network resource by URL (requires sockets).
+
+
+.. index::
+   single: WWW
+   single: World Wide Web
+   single: URL
+
+This module provides a high-level interface for fetching data across the World
+Wide Web.  In particular, the :func:`urlopen` function is similar to the
+built-in function :func:`open`, 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.
+
+It defines the following public functions:
+
+
+.. function:: urlopen(url[, data[, proxies]])
+
+   Open a network object denoted by a URL for reading.  If the URL does not have a
+   scheme identifier, or if it has :file:`file:` 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
+   :exc:`IOError` exception is raised.  If all went well, a file-like object is
+   returned.  This supports the following methods: :meth:`read`, :meth:`readline`,
+   :meth:`readlines`, :meth:`fileno`, :meth:`close`, :meth:`info` and
+   :meth:`geturl`.  It also has proper support for the iterator protocol. One
+   caveat: the :meth:`read` 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 :meth:`info` and :meth:`geturl` methods, these methods have the
+   same interface as for file objects --- see section :ref:`bltin-file-objects` 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.)
+
+   .. index:: module: mimetools
+
+   The :meth:`info` method returns an instance of the class
+   :class:`mimetools.Message` 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'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 :mod:`mimetools` module.
+
+   The :meth:`geturl` method returns the real URL of the page.  In some cases, the
+   HTTP server redirects a client to another URL.  The :func:`urlopen` function
+   handles this transparently, but in some cases the caller needs to know which URL
+   the client was redirected to.  The :meth:`geturl` method can be used to get at
+   this redirected URL.
+
+   If the *url* uses the :file:`http:` scheme identifier, the optional *data*
+   argument may be given to specify a ``POST`` request (normally the request type
+   is ``GET``).  The *data* argument must be in standard
+   :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
+   function below.
+
+   The :func:`urlopen` function works transparently with proxies which do not
+   require authentication.  In a Unix or Windows environment, set the
+   :envvar:`http_proxy`, or :envvar:`ftp_proxy` environment variables to a URL that
+   identifies the proxy server before starting the Python interpreter.  For example
+   (the ``'%'`` is the command prompt)::
+
+      % http_proxy="http://www.someproxy.com:3128"
+      % export http_proxy
+      % python
+      ...
+
+   In a Windows environment, if no proxy environment variables are set, proxy
+   settings are obtained from the registry's Internet Settings section.
+
+   .. index:: single: Internet Config
+
+   In a Macintosh environment, :func:`urlopen` will retrieve proxy information from
+   Internet Config.
+
+   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 ``None`` (the default value)
+   causes environmental proxy settings to be used as discussed above.  For
+   example::
+
+      # Use http://www.someproxy.com:3128 for http proxying
+      proxies = {'http': 'http://www.someproxy.com:3128'}
+      filehandle = urllib.urlopen(some_url, proxies=proxies)
+      # Don'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)
+
+   The :func:`urlopen` function does not support explicit proxy specification.  If
+   you need to override environmental proxy settings, use :class:`URLopener`, or a
+   subclass such as :class:`FancyURLopener`.
+
+   Proxies which require authentication for use are not currently supported; this
+   is considered an implementation limitation.
+
+   .. versionchanged:: 2.3
+      Added the *proxies* support.
+
+
+.. function:: urlretrieve(url[, filename[, reporthook[, data]]])
+
+   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 ``(filename, headers)`` where *filename* is the
+   local file name under which the object can be found, and *headers* is whatever
+   the :meth:`info` method of the object returned by :func:`urlopen` returned (for
+   a remote object, possibly cached). Exceptions are the same as for
+   :func:`urlopen`.
+
+   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 ``-1`` on older FTP servers which do not return a file
+   size in response to a retrieval request.
+
+   If the *url* uses the :file:`http:` scheme identifier, the optional *data*
+   argument may be given to specify a ``POST`` request (normally the request type
+   is ``GET``).  The *data* argument must in standard
+   :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
+   function below.
+
+   .. versionchanged:: 2.5
+      :func:`urlretrieve` will raise :exc:`ContentTooShortError` 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'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
+      :attr:`content` 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.
+
+
+.. data:: _urlopener
+
+   The public functions :func:`urlopen` and :func:`urlretrieve` create an instance
+   of the :class:`FancyURLopener` class and use it to perform their requested
+   actions.  To override this functionality, programmers can create a subclass of
+   :class:`URLopener` or :class:`FancyURLopener`, then assign an instance of that
+   class to the ``urllib._urlopener`` variable before calling the desired function.
+   For example, applications may want to specify a different
+   :mailheader:`User-Agent` header than :class:`URLopener` defines.  This can be
+   accomplished with the following code::
+
+      import urllib
+
+      class AppURLopener(urllib.FancyURLopener):
+          version = "App/1.7"
+
+      urllib._urlopener = AppURLopener()
+
+
+.. function:: urlcleanup()
+
+   Clear the cache that may have been built up by previous calls to
+   :func:`urlretrieve`.
+
+
+.. function:: quote(string[, safe])
+
+   Replace special characters in *string* using the ``%xx`` escape. Letters,
+   digits, and the characters ``'_.-'`` are never quoted. The optional *safe*
+   parameter specifies additional characters that should not be quoted --- its
+   default value is ``'/'``.
+
+   Example: ``quote('/~connolly/')`` yields ``'/%7econnolly/'``.
+
+
+.. function:: quote_plus(string[, safe])
+
+   Like :func:`quote`, 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 *safe*.  It also does not have *safe* default to ``'/'``.
+
+
+.. function:: unquote(string)
+
+   Replace ``%xx`` escapes by their single-character equivalent.
+
+   Example: ``unquote('/%7Econnolly/')`` yields ``'/~connolly/'``.
+
+
+.. function:: unquote_plus(string)
+
+   Like :func:`unquote`, but also replaces plus signs by spaces, as required for
+   unquoting HTML form values.
+
+
+.. function:: urlencode(query[, doseq])
+
+   Convert a mapping object or a sequence of two-element tuples  to a "url-encoded"
+   string, suitable to pass to :func:`urlopen` above as the optional *data*
+   argument.  This is useful to pass a dictionary of form fields to a ``POST``
+   request.  The resulting string is a series of ``key=value`` pairs separated by
+   ``'&'`` characters, where both *key* and *value* are quoted using
+   :func:`quote_plus` above.  If the optional parameter *doseq* is present and
+   evaluates to true, individual ``key=value`` pairs are generated for each element
+   of the sequence. 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 order of parameters in the encoded string will match the order of parameter
+   tuples in the sequence. The :mod:`cgi` module provides the functions
+   :func:`parse_qs` and :func:`parse_qsl` which are used to parse query strings
+   into Python data structures.
+
+
+.. function:: pathname2url(path)
+
+   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 :func:`quote` function.
+
+
+.. function:: url2pathname(path)
+
+   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 :func:`unquote`
+   to decode *path*.
+
+
+.. class:: URLopener([proxies[, **x509]])
+
+   Base class for opening and reading URLs.  Unless you need to support opening
+   objects using schemes other than :file:`http:`, :file:`ftp:`, or :file:`file:`,
+   you probably want to use :class:`FancyURLopener`.
+
+   By default, the :class:`URLopener` class sends a :mailheader:`User-Agent` header
+   of ``urllib/VVV``, where *VVV* is the :mod:`urllib` version number.
+   Applications can define their own :mailheader:`User-Agent` header by subclassing
+   :class:`URLopener` or :class:`FancyURLopener` and setting the class attribute
+   :attr:`version` 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 ``None``, in which case environmental proxy settings will be used if
+   present, as discussed in the definition of :func:`urlopen`, above.
+
+   Additional keyword parameters, collected in *x509*, may be used for
+   authentication of the client when using the :file:`https:` scheme.  The keywords
+   *key_file* and *cert_file* are supported to provide an  SSL key and certificate;
+   both are needed to support client authentication.
+
+   :class:`URLopener` objects will raise an :exc:`IOError` exception if the server
+   returns an error code.
+
+
+.. class:: FancyURLopener(...)
+
+   :class:`FancyURLopener` subclasses :class:`URLopener` providing default handling
+   for the following HTTP response codes: 301, 302, 303, 307 and 401.  For the 30x
+   response codes listed above, the :mailheader:`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 :meth:`http_error_default` is called
+   which you can override in subclasses to handle the error appropriately.
+
+   .. note::
+
+      According to the letter of :rfc:`2616`, 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 :mod:`urllib` reproduces this behaviour.
+
+   The parameters to the constructor are the same as those for :class:`URLopener`.
+
+   .. note::
+
+      When performing basic authentication, a :class:`FancyURLopener` instance calls
+      its :meth:`prompt_user_passwd` 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.
+
+
+.. exception:: ContentTooShortError(msg[, content])
+
+   This exception is raised when the :func:`urlretrieve` function detects that the
+   amount of the downloaded data is less than the  expected amount (given by the
+   *Content-Length* header). The :attr:`content` attribute stores the downloaded
+   (and supposedly truncated) data.
+
+   .. versionadded:: 2.5
+
+Restrictions:
+
+  .. index::
+     pair: HTTP; protocol
+     pair: FTP; protocol
+
+* Currently, only the following protocols are supported: HTTP, (versions 0.9 and
+  1.0),  FTP, and local files.
+
+* The caching feature of :func:`urlretrieve` has been disabled until I find the
+  time to hack proper processing of Expiration time headers.
+
+* There should be a function to query whether a particular URL is in the cache.
+
+* For backward compatibility, if a URL appears to point to a local file but the
+  file can't be opened, the URL is re-interpreted using the FTP protocol.  This
+  can sometimes cause confusing error messages.
+
+* The :func:`urlopen` and :func:`urlretrieve` 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.
+
+  .. index::
+     single: HTML
+     pair: HTTP; protocol
+     module: htmllib
+
+* The data returned by :func:`urlopen` or :func:`urlretrieve` 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 :mailheader:`Content-Type`
+  header.  If the returned data is HTML, you can use the module :mod:`htmllib` to
+  parse it.
+
+  .. index:: single: FTP
+
+* 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 ``/``, 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 ``/`` 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 :mod:`ftplib` module, subclassing :class:`FancyURLOpener`, or changing
+  *_urlopener* to meet your needs.
+
+* This module does not support the use of proxies which require authentication.
+  This may be implemented in the future.
+
+  .. index:: module: urlparse
+
+* Although the :mod:`urllib` module contains (undocumented) routines to parse
+  and unparse URL strings, the recommended interface for URL manipulation is in
+  module :mod:`urlparse`.
+
+
+.. _urlopener-objs:
+
+URLopener Objects
+-----------------
+
+.. sectionauthor:: Skip Montanaro <skip@mojam.com>
+
+
+:class:`URLopener` and :class:`FancyURLopener` objects have the following
+attributes.
+
+
+.. method:: URLopener.open(fullurl[, data])
+
+   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, :meth:`open_unknown` is called.
+   The *data* argument has the same meaning as the *data* argument of
+   :func:`urlopen`.
+
+
+.. method:: URLopener.open_unknown(fullurl[, data])
+
+   Overridable interface to open unknown URL types.
+
+
+.. method:: URLopener.retrieve(url[, filename[, reporthook[, data]]])
+
+   Retrieves the contents of *url* and places it in *filename*.  The return value
+   is a tuple consisting of a local filename and either a
+   :class:`mimetools.Message` object containing the response headers (for remote
+   URLs) or ``None`` (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 :func:`tempfile.mktemp`
+   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 :file:`http:` scheme identifier, the optional *data*
+   argument may be given to specify a ``POST`` request (normally the request type
+   is ``GET``).  The *data* argument must in standard
+   :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
+   function below.
+
+
+.. attribute:: URLopener.version
+
+   Variable that specifies the user agent of the opener object.  To get
+   :mod:`urllib` 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.
+
+The :class:`FancyURLopener` class offers one additional method that should be
+overloaded to provide the appropriate behavior:
+
+
+.. method:: FancyURLopener.prompt_user_passwd(host, realm)
+
+   Return information needed to authenticate the user at the given host in the
+   specified security realm.  The return value should be a tuple, ``(user,
+   password)``, 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.
+
+
+.. _urllib-examples:
+
+Examples
+--------
+
+Here is an example session that uses the ``GET`` method to retrieve a URL
+containing parameters::
+
+   >>> import urllib
+   >>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
+   >>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query?%s" % params)
+   >>> print f.read()
+
+The following example uses the ``POST`` method instead::
+
+   >>> import urllib
+   >>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
+   >>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query", params)
+   >>> print f.read()
+
+The following example uses an explicitly specified HTTP proxy, overriding
+environment settings::
+
+   >>> import urllib
+   >>> proxies = {'http': 'http://proxy.example.com:8080/'}
+   >>> opener = urllib.FancyURLopener(proxies)
+   >>> f = opener.open("http://www.python.org")
+   >>> f.read()
+
+The following example uses no proxies at all, overriding environment settings::
+
+   >>> import urllib
+   >>> opener = urllib.FancyURLopener({})
+   >>> f = opener.open("http://www.python.org/")
+   >>> f.read()
+