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/Doc/library/htmlparser.rst

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  1
  2:mod:`HTMLParser` --- Simple HTML and XHTML parser
  3==================================================
  4
  5.. module:: HTMLParser
  6   :synopsis: A simple parser that can handle HTML and XHTML.
  7
  8.. note::
  9
 10   The :mod:`HTMLParser` module has been renamed to :mod:`html.parser` in Python
 11   3.0.  The :term:`2to3` tool will automatically adapt imports when converting
 12   your sources to 3.0.
 13
 14
 15.. versionadded:: 2.2
 16
 17.. index::
 18   single: HTML
 19   single: XHTML
 20
 21This module defines a class :class:`HTMLParser` which serves as the basis for
 22parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.
 23Unlike the parser in :mod:`htmllib`, this parser is not based on the SGML parser
 24in :mod:`sgmllib`.
 25
 26
 27.. class:: HTMLParser()
 28
 29   The :class:`HTMLParser` class is instantiated without arguments.
 30
 31   An :class:`HTMLParser` instance is fed HTML data and calls handler functions when tags
 32   begin and end.  The :class:`HTMLParser` class is meant to be overridden by the
 33   user to provide a desired behavior.
 34
 35   Unlike the parser in :mod:`htmllib`, this parser does not check that end tags
 36   match start tags or call the end-tag handler for elements which are closed
 37   implicitly by closing an outer element.
 38
 39An exception is defined as well:
 40
 41
 42.. exception:: HTMLParseError
 43
 44   Exception raised by the :class:`HTMLParser` class when it encounters an error
 45   while parsing.  This exception provides three attributes: :attr:`msg` is a brief
 46   message explaining the error, :attr:`lineno` is the number of the line on which
 47   the broken construct was detected, and :attr:`offset` is the number of
 48   characters into the line at which the construct starts.
 49
 50:class:`HTMLParser` instances have the following methods:
 51
 52
 53.. method:: HTMLParser.reset()
 54
 55   Reset the instance.  Loses all unprocessed data.  This is called implicitly at
 56   instantiation time.
 57
 58
 59.. method:: HTMLParser.feed(data)
 60
 61   Feed some text to the parser.  It is processed insofar as it consists of
 62   complete elements; incomplete data is buffered until more data is fed or
 63   :meth:`close` is called.
 64
 65
 66.. method:: HTMLParser.close()
 67
 68   Force processing of all buffered data as if it were followed by an end-of-file
 69   mark.  This method may be redefined by a derived class to define additional
 70   processing at the end of the input, but the redefined version should always call
 71   the :class:`HTMLParser` base class method :meth:`close`.
 72
 73
 74.. method:: HTMLParser.getpos()
 75
 76   Return current line number and offset.
 77
 78
 79.. method:: HTMLParser.get_starttag_text()
 80
 81   Return the text of the most recently opened start tag.  This should not normally
 82   be needed for structured processing, but may be useful in dealing with HTML "as
 83   deployed" or for re-generating input with minimal changes (whitespace between
 84   attributes can be preserved, etc.).
 85
 86
 87.. method:: HTMLParser.handle_starttag(tag, attrs)
 88
 89   This method is called to handle the start of a tag.  It is intended to be
 90   overridden by a derived class; the base class implementation does nothing.
 91
 92   The *tag* argument is the name of the tag converted to lower case. The *attrs*
 93   argument is a list of ``(name, value)`` pairs containing the attributes found
 94   inside the tag's ``<>`` brackets.  The *name* will be translated to lower case,
 95   and quotes in the *value* have been removed, and character and entity references
 96   have been replaced.  For instance, for the tag ``<A
 97   HREF="http://www.cwi.nl/">``, this method would be called as
 98   ``handle_starttag('a', [('href', 'http://www.cwi.nl/')])``.
 99
100   .. versionchanged:: 2.6
101      All entity references from :mod:`htmlentitydefs` are now replaced in the attribute
102      values.
103
104
105.. method:: HTMLParser.handle_startendtag(tag, attrs)
106
107   Similar to :meth:`handle_starttag`, but called when the parser encounters an
108   XHTML-style empty tag (``<a .../>``).  This method may be overridden by
109   subclasses which require this particular lexical information; the default
110   implementation simple calls :meth:`handle_starttag` and :meth:`handle_endtag`.
111
112
113.. method:: HTMLParser.handle_endtag(tag)
114
115   This method is called to handle the end tag of an element.  It is intended to be
116   overridden by a derived class; the base class implementation does nothing.  The
117   *tag* argument is the name of the tag converted to lower case.
118
119
120.. method:: HTMLParser.handle_data(data)
121
122   This method is called to process arbitrary data.  It is intended to be
123   overridden by a derived class; the base class implementation does nothing.
124
125
126.. method:: HTMLParser.handle_charref(name)
127
128   This method is called to process a character reference of the form ``&#ref;``.
129   It is intended to be overridden by a derived class; the base class
130   implementation does nothing.
131
132
133.. method:: HTMLParser.handle_entityref(name)
134
135   This method is called to process a general entity reference of the form
136   ``&name;`` where *name* is an general entity reference.  It is intended to be
137   overridden by a derived class; the base class implementation does nothing.
138
139
140.. method:: HTMLParser.handle_comment(data)
141
142   This method is called when a comment is encountered.  The *comment* argument is
143   a string containing the text between the ``--`` and ``--`` delimiters, but not
144   the delimiters themselves.  For example, the comment ``<!--text-->`` will cause
145   this method to be called with the argument ``'text'``.  It is intended to be
146   overridden by a derived class; the base class implementation does nothing.
147
148
149.. method:: HTMLParser.handle_decl(decl)
150
151   Method called when an SGML declaration is read by the parser.  The *decl*
152   parameter will be the entire contents of the declaration inside the ``<!``...\
153   ``>`` markup.  It is intended to be overridden by a derived class; the base
154   class implementation does nothing.
155
156
157.. method:: HTMLParser.handle_pi(data)
158
159   Method called when a processing instruction is encountered.  The *data*
160   parameter will contain the entire processing instruction. For example, for the
161   processing instruction ``<?proc color='red'>``, this method would be called as
162   ``handle_pi("proc color='red'")``.  It is intended to be overridden by a derived
163   class; the base class implementation does nothing.
164
165   .. note::
166
167      The :class:`HTMLParser` class uses the SGML syntactic rules for processing
168      instructions.  An XHTML processing instruction using the trailing ``'?'`` will
169      cause the ``'?'`` to be included in *data*.
170
171
172.. _htmlparser-example:
173
174Example HTML Parser Application
175-------------------------------
176
177As a basic example, below is a very basic HTML parser that uses the
178:class:`HTMLParser` class to print out tags as they are encountered::
179
180   from HTMLParser import HTMLParser
181
182   class MyHTMLParser(HTMLParser):
183
184       def handle_starttag(self, tag, attrs):
185           print "Encountered the beginning of a %s tag" % tag
186
187       def handle_endtag(self, tag):
188           print "Encountered the end of a %s tag" % tag
189