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  1:mod:`urllib` --- Open arbitrary resources by URL
  2=================================================
  3
  4.. module:: urllib
  5   :synopsis: Open an arbitrary network resource by URL (requires sockets).
  6
  7.. note::
  8    The :mod:`urllib` module has been split into parts and renamed in
  9    Python 3.0 to :mod:`urllib.request`, :mod:`urllib.parse`,
 10    and :mod:`urllib.error`. The :term:`2to3` tool will automatically adapt
 11    imports when converting your sources to 3.0.
 12    Also note that the :func:`urllib.urlopen` function has been removed in
 13    Python 3.0 in favor of :func:`urllib2.urlopen`.
 14
 15.. index::
 16   single: WWW
 17   single: World Wide Web
 18   single: URL
 19
 20This module provides a high-level interface for fetching data across the World
 21Wide Web.  In particular, the :func:`urlopen` function is similar to the
 22built-in function :func:`open`, but accepts Universal Resource Locators (URLs)
 23instead of filenames.  Some restrictions apply --- it can only open URLs for
 24reading, and no seek operations are available.
 25
 26High-level interface
 27--------------------
 28
 29.. function:: urlopen(url[, data[, proxies]])
 30
 31   Open a network object denoted by a URL for reading.  If the URL does not have a
 32   scheme identifier, or if it has :file:`file:` as its scheme identifier, this
 33   opens a local file (without universal newlines); otherwise it opens a socket to
 34   a server somewhere on the network.  If the connection cannot be made the
 35   :exc:`IOError` exception is raised.  If all went well, a file-like object is
 36   returned.  This supports the following methods: :meth:`read`, :meth:`readline`,
 37   :meth:`readlines`, :meth:`fileno`, :meth:`close`, :meth:`info`, :meth:`getcode` and
 38   :meth:`geturl`.  It also has proper support for the :term:`iterator` protocol. One
 39   caveat: the :meth:`read` method, if the size argument is omitted or negative,
 40   may not read until the end of the data stream; there is no good way to determine
 41   that the entire stream from a socket has been read in the general case.
 42
 43   Except for the :meth:`info`, :meth:`getcode` and :meth:`geturl` methods,
 44   these methods have the same interface as for file objects --- see section
 45   :ref:`bltin-file-objects` in this manual.  (It is not a built-in file object,
 46   however, so it can't be used at those few places where a true built-in file
 47   object is required.)
 48
 49   .. index:: module: mimetools
 50
 51   The :meth:`info` method returns an instance of the class
 52   :class:`httplib.HTTPMessage` containing meta-information associated with the
 53   URL.  When the method is HTTP, these headers are those returned by the server
 54   at the head of the retrieved HTML page (including Content-Length and
 55   Content-Type).  When the method is FTP, a Content-Length header will be
 56   present if (as is now usual) the server passed back a file length in response
 57   to the FTP retrieval request. A Content-Type header will be present if the
 58   MIME type can be guessed.  When the method is local-file, returned headers
 59   will include a Date representing the file's last-modified time, a
 60   Content-Length giving file size, and a Content-Type containing a guess at the
 61   file's type. See also the description of the :mod:`mimetools` module.
 62
 63   The :meth:`geturl` method returns the real URL of the page.  In some cases, the
 64   HTTP server redirects a client to another URL.  The :func:`urlopen` function
 65   handles this transparently, but in some cases the caller needs to know which URL
 66   the client was redirected to.  The :meth:`geturl` method can be used to get at
 67   this redirected URL.
 68
 69   The :meth:`getcode` method returns the HTTP status code that was sent with the
 70   response, or ``None`` if the URL is no HTTP URL.
 71
 72   If the *url* uses the :file:`http:` scheme identifier, the optional *data*
 73   argument may be given to specify a ``POST`` request (normally the request type
 74   is ``GET``).  The *data* argument must be in standard
 75   :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
 76   function below.
 77
 78   The :func:`urlopen` function works transparently with proxies which do not
 79   require authentication.  In a Unix or Windows environment, set the
 80   :envvar:`http_proxy`, or :envvar:`ftp_proxy` environment variables to a URL that
 81   identifies the proxy server before starting the Python interpreter.  For example
 82   (the ``'%'`` is the command prompt)::
 83
 84      % http_proxy="http://www.someproxy.com:3128"
 85      % export http_proxy
 86      % python
 87      ...
 88
 89   The :envvar:`no_proxy` environment variable can be used to specify hosts which
 90   shouldn't be reached via proxy; if set, it should be a comma-separated list
 91   of hostname suffixes, optionally with ``:port`` appended, for example
 92   ``cern.ch,ncsa.uiuc.edu,some.host:8080``.
 93
 94   In a Windows environment, if no proxy environment variables are set, proxy
 95   settings are obtained from the registry's Internet Settings section.
 96
 97   .. index:: single: Internet Config
 98
 99   In a Mac OS X  environment, :func:`urlopen` will retrieve proxy information
100   from the OS X System Configuration Framework, which can be managed with
101   Network System Preferences panel.
102
103
104   Alternatively, the optional *proxies* argument may be used to explicitly specify
105   proxies.  It must be a dictionary mapping scheme names to proxy URLs, where an
106   empty dictionary causes no proxies to be used, and ``None`` (the default value)
107   causes environmental proxy settings to be used as discussed above.  For
108   example::
109
110      # Use http://www.someproxy.com:3128 for http proxying
111      proxies = {'http': 'http://www.someproxy.com:3128'}
112      filehandle = urllib.urlopen(some_url, proxies=proxies)
113      # Don't use any proxies
114      filehandle = urllib.urlopen(some_url, proxies={})
115      # Use proxies from environment - both versions are equivalent
116      filehandle = urllib.urlopen(some_url, proxies=None)
117      filehandle = urllib.urlopen(some_url)
118
119   Proxies which require authentication for use are not currently supported; this
120   is considered an implementation limitation.
121
122   .. versionchanged:: 2.3
123      Added the *proxies* support.
124
125   .. versionchanged:: 2.6
126      Added :meth:`getcode` to returned object and support for the
127      :envvar:`no_proxy` environment variable.
128
129   .. deprecated:: 2.6
130      The :func:`urlopen` function has been removed in Python 3.0 in favor
131      of :func:`urllib2.urlopen`.
132
133
134.. function:: urlretrieve(url[, filename[, reporthook[, data]]])
135
136   Copy a network object denoted by a URL to a local file, if necessary. If the URL
137   points to a local file, or a valid cached copy of the object exists, the object
138   is not copied.  Return a tuple ``(filename, headers)`` where *filename* is the
139   local file name under which the object can be found, and *headers* is whatever
140   the :meth:`info` method of the object returned by :func:`urlopen` returned (for
141   a remote object, possibly cached). Exceptions are the same as for
142   :func:`urlopen`.
143
144   The second argument, if present, specifies the file location to copy to (if
145   absent, the location will be a tempfile with a generated name). The third
146   argument, if present, is a hook function that will be called once on
147   establishment of the network connection and once after each block read
148   thereafter.  The hook will be passed three arguments; a count of blocks
149   transferred so far, a block size in bytes, and the total size of the file.  The
150   third argument may be ``-1`` on older FTP servers which do not return a file
151   size in response to a retrieval request.
152
153   If the *url* uses the :file:`http:` scheme identifier, the optional *data*
154   argument may be given to specify a ``POST`` request (normally the request type
155   is ``GET``).  The *data* argument must in standard
156   :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
157   function below.
158
159   .. versionchanged:: 2.5
160      :func:`urlretrieve` will raise :exc:`ContentTooShortError` when it detects that
161      the amount of data available  was less than the expected amount (which is the
162      size reported by a  *Content-Length* header). This can occur, for example, when
163      the  download is interrupted.
164
165      The *Content-Length* is treated as a lower bound: if there's more data  to read,
166      urlretrieve reads more data, but if less data is available,  it raises the
167      exception.
168
169      You can still retrieve the downloaded data in this case, it is stored  in the
170      :attr:`content` attribute of the exception instance.
171
172      If no *Content-Length* header was supplied, urlretrieve can not check the size
173      of the data it has downloaded, and just returns it.  In this case you just have
174      to assume that the download was successful.
175
176
177.. data:: _urlopener
178
179   The public functions :func:`urlopen` and :func:`urlretrieve` create an instance
180   of the :class:`FancyURLopener` class and use it to perform their requested
181   actions.  To override this functionality, programmers can create a subclass of
182   :class:`URLopener` or :class:`FancyURLopener`, then assign an instance of that
183   class to the ``urllib._urlopener`` variable before calling the desired function.
184   For example, applications may want to specify a different
185   :mailheader:`User-Agent` header than :class:`URLopener` defines.  This can be
186   accomplished with the following code::
187
188      import urllib
189
190      class AppURLopener(urllib.FancyURLopener):
191          version = "App/1.7"
192
193      urllib._urlopener = AppURLopener()
194
195
196.. function:: urlcleanup()
197
198   Clear the cache that may have been built up by previous calls to
199   :func:`urlretrieve`.
200
201
202Utility functions
203-----------------
204
205.. function:: quote(string[, safe])
206
207   Replace special characters in *string* using the ``%xx`` escape. Letters,
208   digits, and the characters ``'_.-'`` are never quoted. The optional *safe*
209   parameter specifies additional characters that should not be quoted --- its
210   default value is ``'/'``.
211
212   Example: ``quote('/~connolly/')`` yields ``'/%7econnolly/'``.
213
214
215.. function:: quote_plus(string[, safe])
216
217   Like :func:`quote`, but also replaces spaces by plus signs, as required for
218   quoting HTML form values.  Plus signs in the original string are escaped unless
219   they are included in *safe*.  It also does not have *safe* default to ``'/'``.
220
221
222.. function:: unquote(string)
223
224   Replace ``%xx`` escapes by their single-character equivalent.
225
226   Example: ``unquote('/%7Econnolly/')`` yields ``'/~connolly/'``.
227
228
229.. function:: unquote_plus(string)
230
231   Like :func:`unquote`, but also replaces plus signs by spaces, as required for
232   unquoting HTML form values.
233
234
235.. function:: urlencode(query[, doseq])
236
237   Convert a mapping object or a sequence of two-element tuples  to a "url-encoded"
238   string, suitable to pass to :func:`urlopen` above as the optional *data*
239   argument.  This is useful to pass a dictionary of form fields to a ``POST``
240   request.  The resulting string is a series of ``key=value`` pairs separated by
241   ``'&'`` characters, where both *key* and *value* are quoted using
242   :func:`quote_plus` above.  If the optional parameter *doseq* is present and
243   evaluates to true, individual ``key=value`` pairs are generated for each element
244   of the sequence. When a sequence of two-element tuples is used as the *query*
245   argument, the first element of each tuple is a key and the second is a value.
246   The order of parameters in the encoded string will match the order of parameter
247   tuples in the sequence. The :mod:`urlparse` module provides the functions
248   :func:`parse_qs` and :func:`parse_qsl` which are used to parse query strings
249   into Python data structures.
250
251
252.. function:: pathname2url(path)
253
254   Convert the pathname *path* from the local syntax for a path to the form used in
255   the path component of a URL.  This does not produce a complete URL.  The return
256   value will already be quoted using the :func:`quote` function.
257
258
259.. function:: url2pathname(path)
260
261   Convert the path component *path* from an encoded URL to the local syntax for a
262   path.  This does not accept a complete URL.  This function uses :func:`unquote`
263   to decode *path*.
264
265
266URL Opener objects
267------------------
268
269.. class:: URLopener([proxies[, **x509]])
270
271   Base class for opening and reading URLs.  Unless you need to support opening
272   objects using schemes other than :file:`http:`, :file:`ftp:`, or :file:`file:`,
273   you probably want to use :class:`FancyURLopener`.
274
275   By default, the :class:`URLopener` class sends a :mailheader:`User-Agent` header
276   of ``urllib/VVV``, where *VVV* is the :mod:`urllib` version number.
277   Applications can define their own :mailheader:`User-Agent` header by subclassing
278   :class:`URLopener` or :class:`FancyURLopener` and setting the class attribute
279   :attr:`version` to an appropriate string value in the subclass definition.
280
281   The optional *proxies* parameter should be a dictionary mapping scheme names to
282   proxy URLs, where an empty dictionary turns proxies off completely.  Its default
283   value is ``None``, in which case environmental proxy settings will be used if
284   present, as discussed in the definition of :func:`urlopen`, above.
285
286   Additional keyword parameters, collected in *x509*, may be used for
287   authentication of the client when using the :file:`https:` scheme.  The keywords
288   *key_file* and *cert_file* are supported to provide an  SSL key and certificate;
289   both are needed to support client authentication.
290
291   :class:`URLopener` objects will raise an :exc:`IOError` exception if the server
292   returns an error code.
293
294    .. method:: open(fullurl[, data])
295
296       Open *fullurl* using the appropriate protocol.  This method sets up cache and
297       proxy information, then calls the appropriate open method with its input
298       arguments.  If the scheme is not recognized, :meth:`open_unknown` is called.
299       The *data* argument has the same meaning as the *data* argument of
300       :func:`urlopen`.
301
302
303    .. method:: open_unknown(fullurl[, data])
304
305       Overridable interface to open unknown URL types.
306
307
308    .. method:: retrieve(url[, filename[, reporthook[, data]]])
309
310       Retrieves the contents of *url* and places it in *filename*.  The return value
311       is a tuple consisting of a local filename and either a
312       :class:`mimetools.Message` object containing the response headers (for remote
313       URLs) or ``None`` (for local URLs).  The caller must then open and read the
314       contents of *filename*.  If *filename* is not given and the URL refers to a
315       local file, the input filename is returned.  If the URL is non-local and
316       *filename* is not given, the filename is the output of :func:`tempfile.mktemp`
317       with a suffix that matches the suffix of the last path component of the input
318       URL.  If *reporthook* is given, it must be a function accepting three numeric
319       parameters.  It will be called after each chunk of data is read from the
320       network.  *reporthook* is ignored for local URLs.
321
322       If the *url* uses the :file:`http:` scheme identifier, the optional *data*
323       argument may be given to specify a ``POST`` request (normally the request type
324       is ``GET``).  The *data* argument must in standard
325       :mimetype:`application/x-www-form-urlencoded` format; see the :func:`urlencode`
326       function below.
327
328
329    .. attribute:: version
330
331       Variable that specifies the user agent of the opener object.  To get
332       :mod:`urllib` to tell servers that it is a particular user agent, set this in a
333       subclass as a class variable or in the constructor before calling the base
334       constructor.
335
336
337.. class:: FancyURLopener(...)
338
339   :class:`FancyURLopener` subclasses :class:`URLopener` providing default handling
340   for the following HTTP response codes: 301, 302, 303, 307 and 401.  For the 30x
341   response codes listed above, the :mailheader:`Location` header is used to fetch
342   the actual URL.  For 401 response codes (authentication required), basic HTTP
343   authentication is performed.  For the 30x response codes, recursion is bounded
344   by the value of the *maxtries* attribute, which defaults to 10.
345
346   For all other response codes, the method :meth:`http_error_default` is called
347   which you can override in subclasses to handle the error appropriately.
348
349   .. note::
350
351      According to the letter of :rfc:`2616`, 301 and 302 responses to POST requests
352      must not be automatically redirected without confirmation by the user.  In
353      reality, browsers do allow automatic redirection of these responses, changing
354      the POST to a GET, and :mod:`urllib` reproduces this behaviour.
355
356   The parameters to the constructor are the same as those for :class:`URLopener`.
357
358   .. note::
359
360      When performing basic authentication, a :class:`FancyURLopener` instance calls
361      its :meth:`prompt_user_passwd` method.  The default implementation asks the
362      users for the required information on the controlling terminal.  A subclass may
363      override this method to support more appropriate behavior if needed.
364
365    The :class:`FancyURLopener` class offers one additional method that should be
366    overloaded to provide the appropriate behavior:
367
368    .. method:: prompt_user_passwd(host, realm)
369
370       Return information needed to authenticate the user at the given host in the
371       specified security realm.  The return value should be a tuple, ``(user,
372       password)``, which can be used for basic authentication.
373
374       The implementation prompts for this information on the terminal; an application
375       should override this method to use an appropriate interaction model in the local
376       environment.
377
378.. exception:: ContentTooShortError(msg[, content])
379
380   This exception is raised when the :func:`urlretrieve` function detects that the
381   amount of the downloaded data is less than the  expected amount (given by the
382   *Content-Length* header). The :attr:`content` attribute stores the downloaded
383   (and supposedly truncated) data.
384
385   .. versionadded:: 2.5
386
387
388:mod:`urllib` Restrictions
389--------------------------
390
391  .. index::
392     pair: HTTP; protocol
393     pair: FTP; protocol
394
395* Currently, only the following protocols are supported: HTTP, (versions 0.9 and
396  1.0),  FTP, and local files.
397
398* The caching feature of :func:`urlretrieve` has been disabled until I find the
399  time to hack proper processing of Expiration time headers.
400
401* There should be a function to query whether a particular URL is in the cache.
402
403* For backward compatibility, if a URL appears to point to a local file but the
404  file can't be opened, the URL is re-interpreted using the FTP protocol.  This
405  can sometimes cause confusing error messages.
406
407* The :func:`urlopen` and :func:`urlretrieve` functions can cause arbitrarily
408  long delays while waiting for a network connection to be set up.  This means
409  that it is difficult to build an interactive Web client using these functions
410  without using threads.
411
412  .. index::
413     single: HTML
414     pair: HTTP; protocol
415     module: htmllib
416
417* The data returned by :func:`urlopen` or :func:`urlretrieve` is the raw data
418  returned by the server.  This may be binary data (such as an image), plain text
419  or (for example) HTML.  The HTTP protocol provides type information in the reply
420  header, which can be inspected by looking at the :mailheader:`Content-Type`
421  header.  If the returned data is HTML, you can use the module :mod:`htmllib` to
422  parse it.
423
424  .. index:: single: FTP
425
426* The code handling the FTP protocol cannot differentiate between a file and a
427  directory.  This can lead to unexpected behavior when attempting to read a URL
428  that points to a file that is not accessible.  If the URL ends in a ``/``, it is
429  assumed to refer to a directory and will be handled accordingly.  But if an
430  attempt to read a file leads to a 550 error (meaning the URL cannot be found or
431  is not accessible, often for permission reasons), then the path is treated as a
432  directory in order to handle the case when a directory is specified by a URL but
433  the trailing ``/`` has been left off.  This can cause misleading results when
434  you try to fetch a file whose read permissions make it inaccessible; the FTP
435  code will try to read it, fail with a 550 error, and then perform a directory
436  listing for the unreadable file. If fine-grained control is needed, consider
437  using the :mod:`ftplib` module, subclassing :class:`FancyURLOpener`, or changing
438  *_urlopener* to meet your needs.
439
440* This module does not support the use of proxies which require authentication.
441  This may be implemented in the future.
442
443  .. index:: module: urlparse
444
445* Although the :mod:`urllib` module contains (undocumented) routines to parse
446  and unparse URL strings, the recommended interface for URL manipulation is in
447  module :mod:`urlparse`.
448
449
450.. _urllib-examples:
451
452Examples
453--------
454
455Here is an example session that uses the ``GET`` method to retrieve a URL
456containing parameters::
457
458   >>> import urllib
459   >>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
460   >>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query?%s" % params)
461   >>> print f.read()
462
463The following example uses the ``POST`` method instead::
464
465   >>> import urllib
466   >>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
467   >>> f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query", params)
468   >>> print f.read()
469
470The following example uses an explicitly specified HTTP proxy, overriding
471environment settings::
472
473   >>> import urllib
474   >>> proxies = {'http': 'http://proxy.example.com:8080/'}
475   >>> opener = urllib.FancyURLopener(proxies)
476   >>> f = opener.open("http://www.python.org")
477   >>> f.read()
478
479The following example uses no proxies at all, overriding environment settings::
480
481   >>> import urllib
482   >>> opener = urllib.FancyURLopener({})
483   >>> f = opener.open("http://www.python.org/")
484   >>> f.read()
485