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(python2.1-lib.info)urllib
Open arbitrary resources by URL
===============================
Open an arbitrary network resource by URL (requires sockets).
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()',
`info()' and `geturl()'.
Except for the `info()' and `geturl()' methods, these methods have
the same interface as for file objects -- see section Note: File
Objectsfile 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.
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 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):
% http_proxy="http://www.someproxy.com:3128"
% export http_proxy
% python
...
In a Macintosh environment, `urlopen()' will retrieve proxy
information from Internet Config.
Proxies which require authentication for use are not currently
supported; this is considered an implementation limitation.
`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 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.
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.
`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(query[, doseq])'
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 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:
class AppURLopener(urllib.FancyURLopener):
def __init__(self, *args):
self.version = "App/1.7"
apply(urllib.FancyURLopener.__init__, (self,) + args)
urllib._urlopener = AppURLopener()
`URLopener([proxies[, **x509]])'
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(...)'
`FancyURLopener' subclasses `URLopener' providing default handling
for the following HTTP response codes: 301, 302 or 401. For 301
and 302 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 and 302 response
codes, recursion is bounded by the value of the MAXTRIES attribute,
which defaults 10.
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 HTTP protocol
provides type information in the reply header, which can be
inspected by looking at the `content-type' header. For the Gopher
protocol, 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 `htmllib' to 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' .
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