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185 lines
6.8 KiB
ReStructuredText
185 lines
6.8 KiB
ReStructuredText
:mod:`html.parser` --- Simple HTML and XHTML parser
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===================================================
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.. module:: html.parser
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:synopsis: A simple parser that can handle HTML and XHTML.
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.. index::
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single: HTML
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single: XHTML
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This module defines a class :class:`HTMLParser` which serves as the basis for
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parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.
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.. class:: HTMLParser()
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The :class:`HTMLParser` class is instantiated without arguments.
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An :class:`HTMLParser` instance is fed HTML data and calls handler functions when tags
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begin and end. The :class:`HTMLParser` class is meant to be overridden by the
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user to provide a desired behavior.
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This parser does not check that end tags match start tags or call the end-tag
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handler for elements which are closed implicitly by closing an outer element.
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An exception is defined as well:
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.. exception:: HTMLParseError
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Exception raised by the :class:`HTMLParser` class when it encounters an error
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while parsing. This exception provides three attributes: :attr:`msg` is a brief
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message explaining the error, :attr:`lineno` is the number of the line on which
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the broken construct was detected, and :attr:`offset` is the number of
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characters into the line at which the construct starts.
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:class:`HTMLParser` instances have the following methods:
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.. method:: HTMLParser.reset()
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Reset the instance. Loses all unprocessed data. This is called implicitly at
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instantiation time.
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.. method:: HTMLParser.feed(data)
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Feed some text to the parser. It is processed insofar as it consists of
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complete elements; incomplete data is buffered until more data is fed or
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:meth:`close` is called.
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.. method:: HTMLParser.close()
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Force processing of all buffered data as if it were followed by an end-of-file
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mark. This method may be redefined by a derived class to define additional
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processing at the end of the input, but the redefined version should always call
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the :class:`HTMLParser` base class method :meth:`close`.
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.. method:: HTMLParser.getpos()
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Return current line number and offset.
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.. method:: HTMLParser.get_starttag_text()
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Return the text of the most recently opened start tag. This should not normally
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be needed for structured processing, but may be useful in dealing with HTML "as
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deployed" or for re-generating input with minimal changes (whitespace between
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attributes can be preserved, etc.).
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.. method:: HTMLParser.handle_starttag(tag, attrs)
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This method is called to handle the start of a tag. It is intended to be
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overridden by a derived class; the base class implementation does nothing.
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The *tag* argument is the name of the tag converted to lower case. The *attrs*
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argument is a list of ``(name, value)`` pairs containing the attributes found
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inside the tag's ``<>`` brackets. The *name* will be translated to lower case,
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and quotes in the *value* have been removed, and character and entity references
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have been replaced. For instance, for the tag ``<A
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HREF="http://www.cwi.nl/">``, this method would be called as
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``handle_starttag('a', [('href', 'http://www.cwi.nl/')])``.
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All entity references from :mod:`html.entities` are replaced in the attribute
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values.
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.. method:: HTMLParser.handle_startendtag(tag, attrs)
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Similar to :meth:`handle_starttag`, but called when the parser encounters an
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XHTML-style empty tag (``<a .../>``). This method may be overridden by
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subclasses which require this particular lexical information; the default
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implementation simple calls :meth:`handle_starttag` and :meth:`handle_endtag`.
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.. method:: HTMLParser.handle_endtag(tag)
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This method is called to handle the end tag of an element. It is intended to be
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overridden by a derived class; the base class implementation does nothing. The
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*tag* argument is the name of the tag converted to lower case.
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.. method:: HTMLParser.handle_data(data)
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This method is called to process arbitrary data. It is intended to be
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overridden by a derived class; the base class implementation does nothing.
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.. method:: HTMLParser.handle_charref(name)
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This method is called to process a character reference of the form ``&#ref;``.
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It is intended to be overridden by a derived class; the base class
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implementation does nothing.
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.. method:: HTMLParser.handle_entityref(name)
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This method is called to process a general entity reference of the form
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``&name;`` where *name* is an general entity reference. It is intended to be
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overridden by a derived class; the base class implementation does nothing.
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.. method:: HTMLParser.handle_comment(data)
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This method is called when a comment is encountered. The *comment* argument is
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a string containing the text between the ``--`` and ``--`` delimiters, but not
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the delimiters themselves. For example, the comment ``<!--text-->`` will cause
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this method to be called with the argument ``'text'``. It is intended to be
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overridden by a derived class; the base class implementation does nothing.
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.. method:: HTMLParser.handle_decl(decl)
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Method called when an SGML declaration is read by the parser. The *decl*
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parameter will be the entire contents of the declaration inside the ``<!``...\
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``>`` markup. It is intended to be overridden by a derived class; the base
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class implementation does nothing.
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.. method:: HTMLParser.handle_pi(data)
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Method called when a processing instruction is encountered. The *data*
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parameter will contain the entire processing instruction. For example, for the
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processing instruction ``<?proc color='red'>``, this method would be called as
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``handle_pi("proc color='red'")``. It is intended to be overridden by a derived
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class; the base class implementation does nothing.
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.. note::
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The :class:`HTMLParser` class uses the SGML syntactic rules for processing
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instructions. An XHTML processing instruction using the trailing ``'?'`` will
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cause the ``'?'`` to be included in *data*.
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.. _htmlparser-example:
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Example HTML Parser Application
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-------------------------------
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As a basic example, below is a very basic HTML parser that uses the
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:class:`HTMLParser` class to print out tags as they are encountered::
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>>> from html.parser import HTMLParser
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>>>
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>>> class MyHTMLParser(HTMLParser):
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... def handle_starttag(self, tag, attrs):
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... print("Encountered a {} start tag".format(tag))
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... def handle_endtag(self, tag):
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... print("Encountered a {} end tag".format(tag))
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...
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>>> page = """<html><h1>Title</h1><p>I'm a paragraph!</p></html>"""
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>>>
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>>> myparser = MyHTMLParser()
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>>> myparser.feed(page)
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Encountered a html start tag
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Encountered a h1 start tag
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Encountered a h1 end tag
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Encountered a p start tag
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Encountered a p end tag
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Encountered a html end tag
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