20.16. "urlparse" — Parse URLs into components
**********************************************

備註: The "urlparse" module is renamed to "urllib.parse" in Python
  3. The *2to3* tool will automatically adapt imports when converting
  your sources to Python 3.

**Source code:** Lib/urlparse.py

======================================================================

This module defines a standard interface to break Uniform Resource
Locator (URL) strings up in components (addressing scheme, network
location, path etc.), to combine the components back into a URL
string, and to convert a 「relative URL」 to an absolute URL given a
「base URL.」

The module has been designed to match the Internet RFC on Relative
Uniform Resource Locators. It supports the following URL schemes:
"file", "ftp", "gopher", "hdl", "http", "https", "imap", "mailto",
"mms", "news",  "nntp", "prospero", "rsync", "rtsp", "rtspu",  "sftp",
"shttp", "sip", "sips", "snews", "svn",  "svn+ssh", "telnet", "wais".

2.5 版新加入: Support for the "sftp" and "sips" schemes.

The "urlparse" module defines the following functions:

urlparse.urlparse(urlstring[, scheme[, allow_fragments]])

   Parse a URL into six components, returning a 6-tuple.  This
   corresponds to the general structure of a URL:
   "scheme://netloc/path;parameters?query#fragment". Each tuple item
   is a string, possibly empty. The components are not broken up in
   smaller parts (for example, the network location is a single
   string), and % escapes are not expanded. The delimiters as shown
   above are not part of the result, except for a leading slash in the
   *path* component, which is retained if present.  For example:

   >>> from urlparse import urlparse
   >>> o = urlparse('http://www.cwi.nl:80/%7Eguido/Python.html')
   >>> o   # doctest: +NORMALIZE_WHITESPACE
   ParseResult(scheme='http', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
               params='', query='', fragment='')
   >>> o.scheme
   'http'
   >>> o.port
   80
   >>> o.geturl()
   'http://www.cwi.nl:80/%7Eguido/Python.html'

   Following the syntax specifications in **RFC 1808**, urlparse
   recognizes a netloc only if it is properly introduced by 『//』.
   Otherwise the input is presumed to be a relative URL and thus to
   start with a path component.

   >>> from urlparse import urlparse
   >>> urlparse('//www.cwi.nl:80/%7Eguido/Python.html')
   ParseResult(scheme='', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
              params='', query='', fragment='')
   >>> urlparse('www.cwi.nl/%7Eguido/Python.html')
   ParseResult(scheme='', netloc='', path='www.cwi.nl/%7Eguido/Python.html',
              params='', query='', fragment='')
   >>> urlparse('help/Python.html')
   ParseResult(scheme='', netloc='', path='help/Python.html', params='',
              query='', fragment='')

   If the *scheme* argument is specified, it gives the default
   addressing scheme, to be used only if the URL does not specify one.
   The default value for this argument is the empty string.

   If the *allow_fragments* argument is false, fragment identifiers
   are not recognized and parsed as part of the preceding component,
   even if the URL’s addressing scheme normally does support them.
   The default value for this argument is "True".

   The return value is actually an instance of a subclass of "tuple".
   This class has the following additional read-only convenience
   attributes:

   +--------------------+---------+----------------------------+------------------------+
   | Attribute          | Index   | Value                      | Value if not present   |
   +====================+=========+============================+========================+
   | "scheme"           | 0       | URL scheme specifier       | *scheme* parameter     |
   +--------------------+---------+----------------------------+------------------------+
   | "netloc"           | 1       | Network location part      | empty string           |
   +--------------------+---------+----------------------------+------------------------+
   | "path"             | 2       | Hierarchical path          | empty string           |
   +--------------------+---------+----------------------------+------------------------+
   | "params"           | 3       | Parameters for last path   | empty string           |
   |                    |         | element                    |                        |
   +--------------------+---------+----------------------------+------------------------+
   | "query"            | 4       | Query component            | empty string           |
   +--------------------+---------+----------------------------+------------------------+
   | "fragment"         | 5       | Fragment identifier        | empty string           |
   +--------------------+---------+----------------------------+------------------------+
   | "username"         |         | User name                  | "None"                 |
   +--------------------+---------+----------------------------+------------------------+
   | "password"         |         | Password                   | "None"                 |
   +--------------------+---------+----------------------------+------------------------+
   | "hostname"         |         | Host name (lower case)     | "None"                 |
   +--------------------+---------+----------------------------+------------------------+
   | "port"             |         | Port number as integer, if | "None"                 |
   |                    |         | present                    |                        |
   +--------------------+---------+----------------------------+------------------------+

   See section Results of urlparse() and urlsplit() for more
   information on the result object.

   Characters in the "netloc" attribute that decompose under NFKC
   normalization (as used by the IDNA encoding) into any of "/", "?",
   "#", "@", or ":" will raise a "ValueError". If the URL is
   decomposed before parsing, or is not a Unicode string, no error
   will be raised.

   2.5 版更變: Added attributes to return value.

   2.7 版更變: Added IPv6 URL parsing capabilities.

   2.7.17 版更變: Characters that affect netloc parsing under NFKC
   normalization will now raise "ValueError".

urlparse.parse_qs(qs[, keep_blank_values[, strict_parsing[, max_num_fields]]])

   Parse a query string given as a string argument (data of type
   *application/x-www-form-urlencoded*).  Data are returned as a
   dictionary.  The dictionary keys are the unique query variable
   names and the values are lists of values for each name.

   The optional argument *keep_blank_values* is a flag indicating
   whether blank values in percent-encoded queries should be treated
   as blank strings.   A true value indicates that blanks should be
   retained as  blank strings.  The default false value indicates that
   blank values are to be ignored and treated as if they were not
   included.

   The optional argument *strict_parsing* is a flag indicating what to
   do with parsing errors.  If false (the default), errors are
   silently ignored.  If true, errors raise a "ValueError" exception.

   The optional argument *max_num_fields* is the maximum number of
   fields to read. If set, then throws a "ValueError" if there are
   more than *max_num_fields* fields read.

   Use the "urllib.urlencode()" function to convert such dictionaries
   into query strings.

   2.6 版新加入: Copied from the "cgi" module.

   2.7.16 版更變: Added *max_num_fields* parameter.

urlparse.parse_qsl(qs[, keep_blank_values[, strict_parsing[, max_num_fields]]])

   Parse a query string given as a string argument (data of type
   *application/x-www-form-urlencoded*).  Data are returned as a list
   of name, value pairs.

   The optional argument *keep_blank_values* is a flag indicating
   whether blank values in percent-encoded queries should be treated
   as blank strings.   A true value indicates that blanks should be
   retained as  blank strings.  The default false value indicates that
   blank values are to be ignored and treated as if they were not
   included.

   The optional argument *strict_parsing* is a flag indicating what to
   do with parsing errors.  If false (the default), errors are
   silently ignored.  If true, errors raise a "ValueError" exception.

   The optional argument *max_num_fields* is the maximum number of
   fields to read. If set, then throws a "ValueError" if there are
   more than *max_num_fields* fields read.

   Use the "urllib.urlencode()" function to convert such lists of
   pairs into query strings.

   2.6 版新加入: Copied from the "cgi" module.

   2.7.16 版更變: Added *max_num_fields* parameter.

urlparse.urlunparse(parts)

   Construct a URL from a tuple as returned by "urlparse()". The
   *parts* argument can be any six-item iterable. This may result in a
   slightly different, but equivalent URL, if the URL that was parsed
   originally had unnecessary delimiters (for example, a ? with an
   empty query; the RFC states that these are equivalent).

urlparse.urlsplit(urlstring[, scheme[, allow_fragments]])

   This is similar to "urlparse()", but does not split the params from
   the URL. This should generally be used instead of "urlparse()" if
   the more recent URL syntax allowing parameters to be applied to
   each segment of the *path* portion of the URL (see **RFC 2396**) is
   wanted.  A separate function is needed to separate the path
   segments and parameters.  This function returns a 5-tuple:
   (addressing scheme, network location, path, query, fragment
   identifier).

   The return value is actually an instance of a subclass of "tuple".
   This class has the following additional read-only convenience
   attributes:

   +--------------------+---------+---------------------------+------------------------+
   | Attribute          | Index   | Value                     | Value if not present   |
   +====================+=========+===========================+========================+
   | "scheme"           | 0       | URL scheme specifier      | *scheme* parameter     |
   +--------------------+---------+---------------------------+------------------------+
   | "netloc"           | 1       | Network location part     | empty string           |
   +--------------------+---------+---------------------------+------------------------+
   | "path"             | 2       | Hierarchical path         | empty string           |
   +--------------------+---------+---------------------------+------------------------+
   | "query"            | 3       | Query component           | empty string           |
   +--------------------+---------+---------------------------+------------------------+
   | "fragment"         | 4       | Fragment identifier       | empty string           |
   +--------------------+---------+---------------------------+------------------------+
   | "username"         |         | User name                 | "None"                 |
   +--------------------+---------+---------------------------+------------------------+
   | "password"         |         | Password                  | "None"                 |
   +--------------------+---------+---------------------------+------------------------+
   | "hostname"         |         | Host name (lower case)    | "None"                 |
   +--------------------+---------+---------------------------+------------------------+
   | "port"             |         | Port number as integer,   | "None"                 |
   |                    |         | if present                |                        |
   +--------------------+---------+---------------------------+------------------------+

   See section Results of urlparse() and urlsplit() for more
   information on the result object.

   Characters in the "netloc" attribute that decompose under NFKC
   normalization (as used by the IDNA encoding) into any of "/", "?",
   "#", "@", or ":" will raise a "ValueError". If the URL is
   decomposed before parsing, or is not a Unicode string, no error
   will be raised.

   2.2 版新加入.

   2.5 版更變: Added attributes to return value.

   2.7.17 版更變: Characters that affect netloc parsing under NFKC
   normalization will now raise "ValueError".

urlparse.urlunsplit(parts)

   Combine the elements of a tuple as returned by "urlsplit()" into a
   complete URL as a string. The *parts* argument can be any five-item
   iterable. This may result in a slightly different, but equivalent
   URL, if the URL that was parsed originally had unnecessary
   delimiters (for example, a ? with an empty query; the RFC states
   that these are equivalent).

   2.2 版新加入.

urlparse.urljoin(base, url[, allow_fragments])

   Construct a full (「absolute」) URL by combining a 「base URL」
   (*base*) with another URL (*url*).  Informally, this uses
   components of the base URL, in particular the addressing scheme,
   the network location and (part of) the path, to provide missing
   components in the relative URL.  For example:

   >>> from urlparse import urljoin
   >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html', 'FAQ.html')
   'http://www.cwi.nl/%7Eguido/FAQ.html'

   The *allow_fragments* argument has the same meaning and default as
   for "urlparse()".

   備註: If *url* is an absolute URL (that is, starting with "//" or
     "scheme://"), the *url*’s host name and/or scheme will be present
     in the result.  For example:

      >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html',
      ...         '//www.python.org/%7Eguido')
      'http://www.python.org/%7Eguido'

   If you do not want that behavior, preprocess the *url* with
   "urlsplit()" and "urlunsplit()", removing possible *scheme* and
   *netloc* parts.

urlparse.urldefrag(url)

   If *url* contains a fragment identifier, returns a modified version
   of *url* with no fragment identifier, and the fragment identifier
   as a separate string. If there is no fragment identifier in *url*,
   returns *url* unmodified and an empty string.

也參考:

  **RFC 3986** - Uniform Resource Identifiers
     This is the current standard (STD66). Any changes to urlparse
     module should conform to this. Certain deviations could be
     observed, which are mostly for backward compatibility purposes
     and for certain de-facto parsing requirements as commonly
     observed in major browsers.

  **RFC 2732** - Format for Literal IPv6 Addresses in URL’s.
     This specifies the parsing requirements of IPv6 URLs.

  **RFC 2396** - Uniform Resource Identifiers (URI): Generic Syntax
     Document describing the generic syntactic requirements for both
     Uniform Resource Names (URNs) and Uniform Resource Locators
     (URLs).

  **RFC 2368** - The mailto URL scheme.
     Parsing requirements for mailto URL schemes.

  **RFC 1808** - Relative Uniform Resource Locators
     This Request For Comments includes the rules for joining an
     absolute and a relative URL, including a fair number of 「
     Abnormal Examples」 which govern the treatment of border cases.

  **RFC 1738** - Uniform Resource Locators (URL)
     This specifies the formal syntax and semantics of absolute URLs.


20.16.1. Results of "urlparse()" and "urlsplit()"
=================================================

The result objects from the "urlparse()" and "urlsplit()" functions
are subclasses of the "tuple" type.  These subclasses add the
attributes described in those functions, as well as provide an
additional method:

ParseResult.geturl()

   Return the re-combined version of the original URL as a string.
   This may differ from the original URL in that the scheme will
   always be normalized to lower case and empty components may be
   dropped. Specifically, empty parameters, queries, and fragment
   identifiers will be removed.

   The result of this method is a fixpoint if passed back through the
   original parsing function:

   >>> import urlparse
   >>> url = 'HTTP://www.Python.org/doc/#'

   >>> r1 = urlparse.urlsplit(url)
   >>> r1.geturl()
   'http://www.Python.org/doc/'

   >>> r2 = urlparse.urlsplit(r1.geturl())
   >>> r2.geturl()
   'http://www.Python.org/doc/'

   2.5 版新加入.

The following classes provide the implementations of the parse
results:

class urlparse.ParseResult(scheme, netloc, path, params, query, fragment)

   Concrete class for "urlparse()" results.

class urlparse.SplitResult(scheme, netloc, path, query, fragment)

   Concrete class for "urlsplit()" results.
