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 2.1.7 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
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
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
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
- urlcleanup ()
Clear the cache that may have been built up by previous calls to
- 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 POSTrequest. The resulting string is a series of
key=value pairs separated by "&"
characters, where both key and value are quoted using
- 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
- There should be a function to query whether a particular URL is in
- 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.
- 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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