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.
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(),
info() and geturl().
Except for the info() and geturl() methods,
these methods have the same interface as for
file objects -- see section 2.2.8 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. 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
mimetoolsmodule.
The geturl() method returns the real URL of the page. In
some cases, the HTTP server redirects a client to another URL. The
urlopen() function handles this transparently, but in some
cases the caller needs to know which URL the client was redirected
to. The geturl() method can be used to get at this
redirected URL.
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 be in standard application/x-www-form-urlencoded format;
see the urlencode() function below.
The urlopen() function works transparently with proxies
which do not require authentication. In a Unix or Windows
environment, set the http_proxy, ftp_proxy or
gopher_proxy environment variables to a URL that identifies
the proxy server before starting the Python interpreter. For example
(the "%" is the command prompt):
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 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.
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.
The public functions urlopen() and
urlretrieve() create an instance of the
FancyURLopener class and use it to perform their requested
actions. To override this functionality, programmers can create a
subclass of URLopener or FancyURLopener, then assign
that an instance of that class to the
urllib._urlopener variable before calling the desired function.
For example, applications may want to specify a different
User-Agent: header than URLopener defines. This
can be accomplished with the following code:
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 '/'.
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. It also
does not have safe default to '/'.
Convert a mapping object or a sequence of two-element tuples 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. 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 cgi module provides the functions
parse_qs() and parse_qsl() which are used to
parse query strings into Python data structures.
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
quote() function.
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 unquote() to decode path.
Base class for opening and reading URLs. Unless you need to support
opening objects using schemes other than http:, ftp:,
gopher: or file:, you probably want to use
FancyURLopener.
By default, the URLopener class sends a
User-Agent: header of "urllib/VVV", where
VVV is the urllib version number. Applications can
define their own User-Agent: header by subclassing
URLopener or FancyURLopener and setting the instance
attribute version to an appropriate string value before the
open() method is called.
Additional keyword parameters, collected in x509, are used for
authentication with the https: scheme. The keywords
key_file and cert_file are supported; both are needed to
actually retrieve a resource at an https: URL.
FancyURLopener subclasses URLopener providing default
handling for the following HTTP response codes: 301, 302, 303 and 401.
For 301, 302 and 303 response codes, the Location: header
is used to fetch the actual URL. For 401 response codes
(authentication required), basic HTTP authentication is performed.
For 301, 302 and 303 response codes, recursion is bounded by the value
of the maxtries attribute, which defaults 10.
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
urllib reproduces this behaviour.
The parameters to the constructor are the same as those for
URLopener.
Note:
When performing basic authentication, a
FancyURLopener instance calls its
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.
Restrictions:
Currently, only the following protocols are supported: HTTP, (versions
0.9 and 1.0), Gopher (but not Gopher-+), FTP, and local files.
The caching feature of 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 urlopen() and 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.
The data returned by urlopen() or urlretrieve()
is the raw data returned by the server. This may be binary data
(e.g. an image), plain text or (for example) HTML. The
HTTPprotocol provides type information in the
reply header, which can be inspected by looking at the
Content-Type: header. For the
Gopherprotocol, type information is encoded
in the URL; there is currently no easy way to extract it. If the
returned data is HTML, you can use the module
htmllibto parse it.
This module does not support the use of proxies which require
authentication. This may be implemented in the future.
Although the urllib module contains (undocumented) routines
to parse and unparse URL strings, the recommended interface for URL
manipulation is in module urlparse.
