Doc/library/html.parser.rst - platform/external/python/cpython3 - Gitiles

 :mod:`html.parser` --- Simple HTML and XHTML parser
 ===================================================

 .. module:: html.parser
    :synopsis: A simple parser that can handle HTML and XHTML.

 **Source code:** :source:`Lib/html/parser.py`

 .. index::
    single: HTML
    single: XHTML

 --------------

 This module defines a class :class:`HTMLParser` which serves as the basis for
 parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.

 .. class:: HTMLParser(*, convert_charrefs=True)

    Create a parser instance able to parse invalid markup.

    If *convert_charrefs* is ``True`` (the default), all character
    references (except the ones in ``script``/``style`` elements) are
    automatically converted to the corresponding Unicode characters.

    An :class:`.HTMLParser` instance is fed HTML data and calls handler methods
    when start tags, end tags, text, comments, and other markup elements are
    encountered.  The user should subclass :class:`.HTMLParser` and override its
    methods to implement the desired behavior.

    This parser does not check that end tags match start tags or call the end-tag
    handler for elements which are closed implicitly by closing an outer element.

    .. versionchanged:: 3.4
       *convert_charrefs* keyword argument added.

    .. versionchanged:: 3.5
       The default value for argument *convert_charrefs* is now ``True``.


 Example HTML Parser Application
 -------------------------------

 As a basic example, below is a simple HTML parser that uses the
 :class:`HTMLParser` class to print out start tags, end tags, and data
 as they are encountered::

    from html.parser import HTMLParser

    class MyHTMLParser(HTMLParser):
        def handle_starttag(self, tag, attrs):
            print("Encountered a start tag:", tag)

        def handle_endtag(self, tag):
            print("Encountered an end tag :", tag)

        def handle_data(self, data):
            print("Encountered some data  :", data)

    parser = MyHTMLParser()
    parser.feed('<html><head><title>Test</title></head>'
                '<body><h1>Parse me!</h1></body></html>')

 The output will then be:

 .. code-block:: none

    Encountered a start tag: html
    Encountered a start tag: head
    Encountered a start tag: title
    Encountered some data  : Test
    Encountered an end tag : title
    Encountered an end tag : head
    Encountered a start tag: body
    Encountered a start tag: h1
    Encountered some data  : Parse me!
    Encountered an end tag : h1
    Encountered an end tag : body
    Encountered an end tag : html


 :class:`.HTMLParser` Methods
 ----------------------------

 :class:`HTMLParser` instances have the following methods:


 .. method:: HTMLParser.feed(data)

    Feed some text to the parser.  It is processed insofar as it consists of
    complete elements; incomplete data is buffered until more data is fed or
    :meth:`close` is called.  *data* must be :class:`str`.


 .. method:: HTMLParser.close()

    Force processing of all buffered data as if it were followed by an end-of-file
    mark.  This method may be redefined by a derived class to define additional
    processing at the end of the input, but the redefined version should always call
    the :class:`HTMLParser` base class method :meth:`close`.


 .. method:: HTMLParser.reset()

    Reset the instance.  Loses all unprocessed data.  This is called implicitly at
    instantiation time.


 .. method:: HTMLParser.getpos()

    Return current line number and offset.


 .. method:: HTMLParser.get_starttag_text()

    Return the text of the most recently opened start tag.  This should not normally
    be needed for structured processing, but may be useful in dealing with HTML "as
    deployed" or for re-generating input with minimal changes (whitespace between
    attributes can be preserved, etc.).


 The following methods are called when data or markup elements are encountered
 and they are meant to be overridden in a subclass.  The base class
 implementations do nothing (except for :meth:`~HTMLParser.handle_startendtag`):


 .. method:: HTMLParser.handle_starttag(tag, attrs)

    This method is called to handle the start of a tag (e.g. ``<div id="main">``).

    The *tag* argument is the name of the tag converted to lower case. The *attrs*
    argument is a list of ``(name, value)`` pairs containing the attributes found
    inside the tag's ``<>`` brackets.  The *name* will be translated to lower case,
    and quotes in the *value* have been removed, and character and entity references
    have been replaced.

    For instance, for the tag ``<A HREF="https://www.cwi.nl/">``, this method
    would be called as ``handle_starttag('a', [('href', 'https://www.cwi.nl/')])``.

    All entity references from :mod:`html.entities` are replaced in the attribute
    values.


 .. method:: HTMLParser.handle_endtag(tag)

    This method is called to handle the end tag of an element (e.g. ``</div>``).

    The *tag* argument is the name of the tag converted to lower case.


 .. method:: HTMLParser.handle_startendtag(tag, attrs)

    Similar to :meth:`handle_starttag`, but called when the parser encounters an
    XHTML-style empty tag (``<img ... />``).  This method may be overridden by
    subclasses which require this particular lexical information; the default
    implementation simply calls :meth:`handle_starttag` and :meth:`handle_endtag`.


 .. method:: HTMLParser.handle_data(data)

    This method is called to process arbitrary data (e.g. text nodes and the
    content of ``<script>...</script>`` and ``<style>...</style>``).


 .. method:: HTMLParser.handle_entityref(name)

    This method is called to process a named character reference of the form
    ``&name;`` (e.g. ``&gt;``), where *name* is a general entity reference
    (e.g. ``'gt'``).  This method is never called if *convert_charrefs* is
    ``True``.


 .. method:: HTMLParser.handle_charref(name)

    This method is called to process decimal and hexadecimal numeric character
    references of the form ``&#NNN;`` and ``&#xNNN;``.  For example, the decimal
    equivalent for ``&gt;`` is ``&#62;``, whereas the hexadecimal is ``&#x3E;``;
    in this case the method will receive ``'62'`` or ``'x3E'``.  This method
    is never called if *convert_charrefs* is ``True``.


 .. method:: HTMLParser.handle_comment(data)

    This method is called when a comment is encountered (e.g. ``<!--comment-->``).

    For example, the comment ``<!-- comment -->`` will cause this method to be
    called with the argument ``' comment '``.

    The content of Internet Explorer conditional comments (condcoms) will also be
    sent to this method, so, for ``<!--[if IE 9]>IE9-specific content<![endif]-->``,
    this method will receive ``'[if IE 9]>IE9-specific content<![endif]'``.


 .. method:: HTMLParser.handle_decl(decl)

    This method is called to handle an HTML doctype declaration (e.g.
    ``<!DOCTYPE html>``).

    The *decl* parameter will be the entire contents of the declaration inside
    the ``<!...>`` markup (e.g. ``'DOCTYPE html'``).


 .. method:: HTMLParser.handle_pi(data)

    Method called when a processing instruction is encountered.  The *data*
    parameter will contain the entire processing instruction. For example, for the
    processing instruction ``<?proc color='red'>``, this method would be called as
    ``handle_pi("proc color='red'")``.  It is intended to be overridden by a derived
    class; the base class implementation does nothing.

    .. note::

       The :class:`HTMLParser` class uses the SGML syntactic rules for processing
       instructions.  An XHTML processing instruction using the trailing ``'?'`` will
       cause the ``'?'`` to be included in *data*.


 .. method:: HTMLParser.unknown_decl(data)

    This method is called when an unrecognized declaration is read by the parser.

    The *data* parameter will be the entire contents of the declaration inside
    the ``<![...]>`` markup.  It is sometimes useful to be overridden by a
    derived class.  The base class implementation does nothing.


 .. _htmlparser-examples:

 Examples
 --------

 The following class implements a parser that will be used to illustrate more
 examples::

    from html.parser import HTMLParser
    from html.entities import name2codepoint

    class MyHTMLParser(HTMLParser):
        def handle_starttag(self, tag, attrs):
            print("Start tag:", tag)
            for attr in attrs:
                print("     attr:", attr)

        def handle_endtag(self, tag):
            print("End tag  :", tag)

        def handle_data(self, data):
            print("Data     :", data)

        def handle_comment(self, data):
            print("Comment  :", data)

        def handle_entityref(self, name):
            c = chr(name2codepoint[name])
            print("Named ent:", c)

        def handle_charref(self, name):
            if name.startswith('x'):
                c = chr(int(name[1:], 16))
            else:
                c = chr(int(name))
            print("Num ent  :", c)

        def handle_decl(self, data):
            print("Decl     :", data)

    parser = MyHTMLParser()

 Parsing a doctype::

    >>> parser.feed('<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" '
    ...             '"http://www.w3.org/TR/html4/strict.dtd">')
    Decl     : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"

 Parsing an element with a few attributes and a title::

    >>> parser.feed('<img src="python-logo.png" alt="The Python logo">')
    Start tag: img
         attr: ('src', 'python-logo.png')
         attr: ('alt', 'The Python logo')
    >>>
    >>> parser.feed('<h1>Python</h1>')
    Start tag: h1
    Data     : Python
    End tag  : h1

 The content of ``script`` and ``style`` elements is returned as is, without
 further parsing::

    >>> parser.feed('<style type="text/css">#python { color: green }</style>')
    Start tag: style
         attr: ('type', 'text/css')
    Data     : #python { color: green }
    End tag  : style

    >>> parser.feed('<script type="text/javascript">'
    ...             'alert("<strong>hello!</strong>");</script>')
    Start tag: script
         attr: ('type', 'text/javascript')
    Data     : alert("<strong>hello!</strong>");
    End tag  : script

 Parsing comments::

    >>> parser.feed('<!-- a comment -->'
    ...             '<!--[if IE 9]>IE-specific content<![endif]-->')
    Comment  :  a comment
    Comment  : [if IE 9]>IE-specific content<![endif]

 Parsing named and numeric character references and converting them to the
 correct char (note: these 3 references are all equivalent to ``'>'``)::

    >>> parser.feed('&gt;&#62;&#x3E;')
    Named ent: >
    Num ent  : >
    Num ent  : >

 Feeding incomplete chunks to :meth:`~HTMLParser.feed` works, but
 :meth:`~HTMLParser.handle_data` might be called more than once
 (unless *convert_charrefs* is set to ``True``)::

    >>> for chunk in ['<sp', 'an>buff', 'ered ', 'text</s', 'pan>']:
    ...     parser.feed(chunk)
    ...
    Start tag: span
    Data     : buff
    Data     : ered
    Data     : text
    End tag  : span

 Parsing invalid HTML (e.g. unquoted attributes) also works::

    >>> parser.feed('<p><a class=link href=#main>tag soup</p ></a>')
    Start tag: p
    Start tag: a
         attr: ('class', 'link')
         attr: ('href', '#main')
    Data     : tag soup
    End tag  : p
    End tag  : a
	:mod:`html.parser` --- Simple HTML and XHTML parser
	===================================================

	.. module:: html.parser
	:synopsis: A simple parser that can handle HTML and XHTML.

	Source code: :source:`Lib/html/parser.py`

	.. index::
	single: HTML
	single: XHTML

	--------------

	This module defines a class :class:`HTMLParser` which serves as the basis for
	parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.

	.. class:: HTMLParser(*, convert_charrefs=True)

	Create a parser instance able to parse invalid markup.

	If convert_charrefs is ``True`` (the default), all character
	references (except the ones in ``script``/``style`` elements) are
	automatically converted to the corresponding Unicode characters.

	An :class:`.HTMLParser` instance is fed HTML data and calls handler methods
	when start tags, end tags, text, comments, and other markup elements are
	encountered. The user should subclass :class:`.HTMLParser` and override its
	methods to implement the desired behavior.

	This parser does not check that end tags match start tags or call the end-tag
	handler for elements which are closed implicitly by closing an outer element.

	.. versionchanged:: 3.4
	convert_charrefs keyword argument added.

	.. versionchanged:: 3.5
	The default value for argument convert_charrefs is now ``True``.


	Example HTML Parser Application
	-------------------------------

	As a basic example, below is a simple HTML parser that uses the
	:class:`HTMLParser` class to print out start tags, end tags, and data
	as they are encountered::

	from html.parser import HTMLParser

	class MyHTMLParser(HTMLParser):
	def handle_starttag(self, tag, attrs):
	print("Encountered a start tag:", tag)

	def handle_endtag(self, tag):
	print("Encountered an end tag :", tag)

	def handle_data(self, data):
	print("Encountered some data :", data)

	parser = MyHTMLParser()
	parser.feed('<html><head><title>Test</title></head>'
	'<body><h1>Parse me!</h1></body></html>')

	The output will then be:

	.. code-block:: none

	Encountered a start tag: html
	Encountered a start tag: head
	Encountered a start tag: title
	Encountered some data : Test
	Encountered an end tag : title
	Encountered an end tag : head
	Encountered a start tag: body
	Encountered a start tag: h1
	Encountered some data : Parse me!
	Encountered an end tag : h1
	Encountered an end tag : body
	Encountered an end tag : html


	:class:`.HTMLParser` Methods
	----------------------------

	:class:`HTMLParser` instances have the following methods:


	.. method:: HTMLParser.feed(data)

	Feed some text to the parser. It is processed insofar as it consists of
	complete elements; incomplete data is buffered until more data is fed or
	:meth:`close` is called. data must be :class:`str`.


	.. method:: HTMLParser.close()

	Force processing of all buffered data as if it were followed by an end-of-file
	mark. This method may be redefined by a derived class to define additional
	processing at the end of the input, but the redefined version should always call
	the :class:`HTMLParser` base class method :meth:`close`.


	.. method:: HTMLParser.reset()

	Reset the instance. Loses all unprocessed data. This is called implicitly at
	instantiation time.


	.. method:: HTMLParser.getpos()

	Return current line number and offset.


	.. method:: HTMLParser.get_starttag_text()

	Return the text of the most recently opened start tag. This should not normally
	be needed for structured processing, but may be useful in dealing with HTML "as
	deployed" or for re-generating input with minimal changes (whitespace between
	attributes can be preserved, etc.).


	The following methods are called when data or markup elements are encountered
	and they are meant to be overridden in a subclass. The base class
	implementations do nothing (except for :meth:`~HTMLParser.handle_startendtag`):


	.. method:: HTMLParser.handle_starttag(tag, attrs)

	This method is called to handle the start of a tag (e.g. ``<div id="main">``).

	The tag argument is the name of the tag converted to lower case. The attrs
	argument is a list of ``(name, value)`` pairs containing the attributes found
	inside the tag's ``<>`` brackets. The name will be translated to lower case,
	and quotes in the value have been removed, and character and entity references
	have been replaced.

	For instance, for the tag ``<A HREF="https://www.cwi.nl/">``, this method
	would be called as ``handle_starttag('a', [('href', 'https://www.cwi.nl/')])``.

	All entity references from :mod:`html.entities` are replaced in the attribute
	values.


	.. method:: HTMLParser.handle_endtag(tag)

	This method is called to handle the end tag of an element (e.g. ``</div>``).

	The tag argument is the name of the tag converted to lower case.


	.. method:: HTMLParser.handle_startendtag(tag, attrs)

	Similar to :meth:`handle_starttag`, but called when the parser encounters an
	XHTML-style empty tag (``<img ... />``). This method may be overridden by
	subclasses which require this particular lexical information; the default
	implementation simply calls :meth:`handle_starttag` and :meth:`handle_endtag`.


	.. method:: HTMLParser.handle_data(data)

	This method is called to process arbitrary data (e.g. text nodes and the
	content of ``<script>...</script>`` and ``<style>...</style>``).


	.. method:: HTMLParser.handle_entityref(name)

	This method is called to process a named character reference of the form
	``&name;`` (e.g. ``>``), where name is a general entity reference
	(e.g. ``'gt'``). This method is never called if convert_charrefs is
	``True``.


	.. method:: HTMLParser.handle_charref(name)

	This method is called to process decimal and hexadecimal numeric character
	references of the form ``&#NNN;`` and ``&#xNNN;``. For example, the decimal
	equivalent for ``>`` is ``>``, whereas the hexadecimal is ``>``;
	in this case the method will receive ``'62'`` or ``'x3E'``. This method
	is never called if convert_charrefs is ``True``.


	.. method:: HTMLParser.handle_comment(data)

	This method is called when a comment is encountered (e.g. ``<!--comment-->``).

	For example, the comment ``<!-- comment -->`` will cause this method to be
	called with the argument ``' comment '``.

	The content of Internet Explorer conditional comments (condcoms) will also be
	sent to this method, so, for ``<!--[if IE 9]>IE9-specific content<![endif]-->``,
	this method will receive ``'[if IE 9]>IE9-specific content<![endif]'``.


	.. method:: HTMLParser.handle_decl(decl)

	This method is called to handle an HTML doctype declaration (e.g.
	``<!DOCTYPE html>``).

	The decl parameter will be the entire contents of the declaration inside
	the ``<!...>`` markup (e.g. ``'DOCTYPE html'``).


	.. method:: HTMLParser.handle_pi(data)

	Method called when a processing instruction is encountered. The data
	parameter will contain the entire processing instruction. For example, for the
	processing instruction ``<?proc color='red'>``, this method would be called as
	``handle_pi("proc color='red'")``. It is intended to be overridden by a derived
	class; the base class implementation does nothing.

	.. note::

	The :class:`HTMLParser` class uses the SGML syntactic rules for processing
	instructions. An XHTML processing instruction using the trailing ``'?'`` will
	cause the ``'?'`` to be included in data.


	.. method:: HTMLParser.unknown_decl(data)

	This method is called when an unrecognized declaration is read by the parser.

	The data parameter will be the entire contents of the declaration inside
	the ``<![...]>`` markup. It is sometimes useful to be overridden by a
	derived class. The base class implementation does nothing.


	.. _htmlparser-examples:

	Examples
	--------

	The following class implements a parser that will be used to illustrate more
	examples::

	from html.parser import HTMLParser
	from html.entities import name2codepoint

	class MyHTMLParser(HTMLParser):
	def handle_starttag(self, tag, attrs):
	print("Start tag:", tag)
	for attr in attrs:
	print(" attr:", attr)

	def handle_endtag(self, tag):
	print("End tag :", tag)

	def handle_data(self, data):
	print("Data :", data)

	def handle_comment(self, data):
	print("Comment :", data)

	def handle_entityref(self, name):
	c = chr(name2codepoint[name])
	print("Named ent:", c)

	def handle_charref(self, name):
	if name.startswith('x'):
	c = chr(int(name[1:], 16))
	else:
	c = chr(int(name))
	print("Num ent :", c)

	def handle_decl(self, data):
	print("Decl :", data)

	parser = MyHTMLParser()

	Parsing a doctype::

	>>> parser.feed('<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" '
	... '"http://www.w3.org/TR/html4/strict.dtd">')
	Decl : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"

	Parsing an element with a few attributes and a title::

	>>> parser.feed('<img src="python-logo.png" alt="The Python logo">')
	Start tag: img
	attr: ('src', 'python-logo.png')
	attr: ('alt', 'The Python logo')
	>>>
	>>> parser.feed('<h1>Python</h1>')
	Start tag: h1
	Data : Python
	End tag : h1

	The content of ``script`` and ``style`` elements is returned as is, without
	further parsing::

	>>> parser.feed('<style type="text/css">#python { color: green }</style>')
	Start tag: style
	attr: ('type', 'text/css')
	Data : #python { color: green }
	End tag : style

	>>> parser.feed('<script type="text/javascript">'
	... 'alert("<strong>hello!</strong>");</script>')
	Start tag: script
	attr: ('type', 'text/javascript')
	Data : alert("<strong>hello!</strong>");
	End tag : script

	Parsing comments::

	>>> parser.feed('<!-- a comment -->'
	... '<!--[if IE 9]>IE-specific content<![endif]-->')
	Comment : a comment
	Comment : [if IE 9]>IE-specific content<![endif]

	Parsing named and numeric character references and converting them to the
	correct char (note: these 3 references are all equivalent to ``'>'``)::

	>>> parser.feed('>>>')
	Named ent: >
	Num ent : >
	Num ent : >

	Feeding incomplete chunks to :meth:`~HTMLParser.feed` works, but
	:meth:`~HTMLParser.handle_data` might be called more than once
	(unless convert_charrefs is set to ``True``)::

	>>> for chunk in ['<sp', 'an>buff', 'ered ', 'text</s', 'pan>']:
	... parser.feed(chunk)
	...
	Start tag: span
	Data : buff
	Data : ered
	Data : text
	End tag : span

	Parsing invalid HTML (e.g. unquoted attributes) also works::

	>>> parser.feed('<p><a class=link href=#main>tag soup</p ></a>')
	Start tag: p
	Start tag: a
	attr: ('class', 'link')
	attr: ('href', '#main')
	Data : tag soup
	End tag : p
	End tag : a