mirror of https://github.com/python/cpython
353 lines
12 KiB
ReStructuredText
353 lines
12 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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**Source code:** :source:`Lib/html/parser.py`
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--------------
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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(strict=False)
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Create a parser instance. If *strict* is ``False`` (the default), the parser
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will accept and parse invalid markup. If *strict* is ``True`` the parser
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will raise an :exc:`~html.parser.HTMLParseError` exception instead [#]_ when
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it's not able to parse the markup.
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The use of ``strict=True`` is discouraged and the *strict* argument is
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deprecated.
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An :class:`.HTMLParser` instance is fed HTML data and calls handler methods
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when start tags, end tags, text, comments, and other markup elements are
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encountered. The user should subclass :class:`.HTMLParser` and override its
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methods to implement the 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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.. versionchanged:: 3.2 *strict* keyword added
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.. deprecated-removed:: 3.3 3.5
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The *strict* argument and the strict mode have been deprecated.
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The parser is now able to accept and parse invalid markup too.
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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 and *strict* is ``True``. This exception provides three
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attributes: :attr:`msg` is a brief message explaining the error,
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:attr:`lineno` is the number of the line on which the broken construct was
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detected, and :attr:`offset` is the number of characters into the line at
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which the construct starts.
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.. deprecated-removed:: 3.3 3.5
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This exception has been deprecated because it's never raised by the parser
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(when the default non-strict mode is used).
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Example HTML Parser Application
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-------------------------------
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As a basic example, below is a simple HTML parser that uses the
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:class:`HTMLParser` class to print out start tags, end tags, and data
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as they are encountered::
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from html.parser import HTMLParser
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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:", tag)
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def handle_endtag(self, tag):
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print("Encountered an end tag :", tag)
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def handle_data(self, data):
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print("Encountered some data :", data)
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parser = MyHTMLParser(strict=False)
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parser.feed('<html><head><title>Test</title></head>'
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'<body><h1>Parse me!</h1></body></html>')
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The output will then be::
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Encountered a start tag: html
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Encountered a start tag: head
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Encountered a start tag: title
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Encountered some data : Test
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Encountered an end tag : title
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Encountered an end tag : head
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Encountered a start tag: body
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Encountered a start tag: h1
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Encountered some data : Parse me!
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Encountered an end tag : h1
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Encountered an end tag : body
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Encountered an end tag : html
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:class:`.HTMLParser` Methods
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----------------------------
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:class:`HTMLParser` instances have the following methods:
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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. *data* must be :class:`str`.
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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.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.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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The following methods are called when data or markup elements are encountered
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and they are meant to be overridden in a subclass. The base class
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implementations do nothing (except for :meth:`~HTMLParser.handle_startendtag`):
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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 (e.g. ``<div id="main">``).
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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.
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For instance, for the tag ``<A HREF="http://www.cwi.nl/">``, this method
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would be called as ``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_endtag(tag)
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This method is called to handle the end tag of an element (e.g. ``</div>``).
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The *tag* argument is the name of the tag converted to lower case.
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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 (``<img ... />``). This method may be overridden by
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subclasses which require this particular lexical information; the default
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implementation simply calls :meth:`handle_starttag` and :meth:`handle_endtag`.
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.. method:: HTMLParser.handle_data(data)
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This method is called to process arbitrary data (e.g. text nodes and the
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content of ``<script>...</script>`` and ``<style>...</style>``).
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.. method:: HTMLParser.handle_entityref(name)
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This method is called to process a named character reference of the form
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``&name;`` (e.g. ``>``), where *name* is a general entity reference
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(e.g. ``'gt'``).
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.. method:: HTMLParser.handle_charref(name)
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This method is called to process decimal and hexadecimal numeric character
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references of the form ``&#NNN;`` and ``&#xNNN;``. For example, the decimal
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equivalent for ``>`` is ``>``, whereas the hexadecimal is ``>``;
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in this case the method will receive ``'62'`` or ``'x3E'``.
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.. method:: HTMLParser.handle_comment(data)
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This method is called when a comment is encountered (e.g. ``<!--comment-->``).
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For example, the comment ``<!-- comment -->`` will cause this method to be
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called with the argument ``' comment '``.
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The content of Internet Explorer conditional comments (condcoms) will also be
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sent to this method, so, for ``<!--[if IE 9]>IE9-specific content<![endif]-->``,
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this method will receive ``'[if IE 9]>IE-specific content<![endif]'``.
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.. method:: HTMLParser.handle_decl(decl)
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This method is called to handle an HTML doctype declaration (e.g.
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``<!DOCTYPE html>``).
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The *decl* parameter will be the entire contents of the declaration inside
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the ``<!...>`` markup (e.g. ``'DOCTYPE html'``).
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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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.. method:: HTMLParser.unknown_decl(data)
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This method is called when an unrecognized declaration is read by the parser.
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The *data* parameter will be the entire contents of the declaration inside
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the ``<![...]>`` markup. It is sometimes useful to be overridden by a
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derived class. The base class implementation raises an :exc:`HTMLParseError`
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when *strict* is ``True``.
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.. _htmlparser-examples:
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Examples
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--------
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The following class implements a parser that will be used to illustrate more
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examples::
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from html.parser import HTMLParser
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from html.entities import name2codepoint
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class MyHTMLParser(HTMLParser):
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def handle_starttag(self, tag, attrs):
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print("Start tag:", tag)
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for attr in attrs:
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print(" attr:", attr)
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def handle_endtag(self, tag):
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print("End tag :", tag)
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def handle_data(self, data):
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print("Data :", data)
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def handle_comment(self, data):
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print("Comment :", data)
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def handle_entityref(self, name):
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c = chr(name2codepoint[name])
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print("Named ent:", c)
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def handle_charref(self, name):
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if name.startswith('x'):
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c = chr(int(name[1:], 16))
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else:
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c = chr(int(name))
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print("Num ent :", c)
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def handle_decl(self, data):
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print("Decl :", data)
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parser = MyHTMLParser(strict=False)
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Parsing a doctype::
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>>> parser.feed('<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" '
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... '"http://www.w3.org/TR/html4/strict.dtd">')
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Decl : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"
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Parsing an element with a few attributes and a title::
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>>> parser.feed('<img src="python-logo.png" alt="The Python logo">')
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Start tag: img
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attr: ('src', 'python-logo.png')
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attr: ('alt', 'The Python logo')
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>>>
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>>> parser.feed('<h1>Python</h1>')
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Start tag: h1
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Data : Python
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End tag : h1
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The content of ``script`` and ``style`` elements is returned as is, without
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further parsing::
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>>> parser.feed('<style type="text/css">#python { color: green }</style>')
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Start tag: style
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attr: ('type', 'text/css')
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Data : #python { color: green }
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End tag : style
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>>>
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>>> parser.feed('<script type="text/javascript">'
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... 'alert("<strong>hello!</strong>");</script>')
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Start tag: script
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attr: ('type', 'text/javascript')
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Data : alert("<strong>hello!</strong>");
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End tag : script
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Parsing comments::
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>>> parser.feed('<!-- a comment -->'
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... '<!--[if IE 9]>IE-specific content<![endif]-->')
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Comment : a comment
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Comment : [if IE 9]>IE-specific content<![endif]
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Parsing named and numeric character references and converting them to the
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correct char (note: these 3 references are all equivalent to ``'>'``)::
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>>> parser.feed('>>>')
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Named ent: >
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Num ent : >
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Num ent : >
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Feeding incomplete chunks to :meth:`~HTMLParser.feed` works, but
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:meth:`~HTMLParser.handle_data` might be called more than once::
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>>> for chunk in ['<sp', 'an>buff', 'ered ', 'text</s', 'pan>']:
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... parser.feed(chunk)
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...
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Start tag: span
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Data : buff
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Data : ered
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Data : text
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End tag : span
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Parsing invalid HTML (e.g. unquoted attributes) also works::
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>>> parser.feed('<p><a class=link href=#main>tag soup</p ></a>')
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Start tag: p
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Start tag: a
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attr: ('class', 'link')
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attr: ('href', '#main')
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Data : tag soup
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End tag : p
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End tag : a
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.. rubric:: Footnotes
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.. [#] For backward compatibility reasons *strict* mode does not raise
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exceptions for all non-compliant HTML. That is, some invalid HTML
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is tolerated even in *strict* mode.
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