11.2 urllib -- Open an arbitrary object given by URL.

This module provides a high-level interface for fetching data across the World-Wide Web. In particular, the urlopen() function is similar to the built-in function 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:

urlopen (url[, data])
Open a network object denoted by a URL for reading. If the URL does not have a scheme identifier, or if it has "file:" 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 IOError exception is raised. If all went well, a file-like object is returned. This supports the following methods: read(), readline(), readlines(), fileno(), close() and info().

Except for the info() method, these methods have the same interface as for file objects -- see section 2.1 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.)

The info() method returns an instance of the 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. 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 mimetools module.

If the url uses the "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 "application/x-www-form-urlencoded" format; see the urlencode() function below.

urlretrieve (url[, filename][, hook])
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 either None (for a local object) or whatever the info() method of the object returned by urlopen() returned (for a remote object, possibly cached). Exceptions are the same as for 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.

urlcleanup ()
Clear the cache that may have been built up by previous calls to urlretrieve().

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/'.

quote_plus (string[, safe])
Like 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.

unquote (string)
Replace "%xx" escapes by their single-character equivalent.

Example: unquote('/%7Econnolly/') yields '/connolly/'.

unquote_plus (string)
Like unquote(), but also replaces plus signs by spaces, as required for unquoting HTML form values.

urlencode (dict)
Convert a dictionary to a ``url-encoded'' string, suitable to pass to 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 quote_plus() above.

Restrictions: