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Commit c39b5526 authored by Ezio Melotti's avatar Ezio Melotti
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#14020: improve HTMLParser documentation.

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Doc/library/htmlparser.rst
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...@@ -22,7 +22,7 @@ ...@@ -22,7 +22,7 @@
-------------- --------------
This module defines a class :class:`HTMLParser` which serves as the basis for 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. parsing text files formatted in HTML (HyperText Mark-up Language) and XHTML.
Unlike the parser in :mod:`htmllib`, this parser is not based on the SGML parser Unlike the parser in :mod:`htmllib`, this parser is not based on the SGML parser
in :mod:`sgmllib`. in :mod:`sgmllib`.
...@@ -30,11 +30,12 @@ in :mod:`sgmllib`. ...@@ -30,11 +30,12 @@ in :mod:`sgmllib`.
.. class:: HTMLParser() .. class:: HTMLParser()
The :class:`HTMLParser` class is instantiated without arguments. 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.
An :class:`HTMLParser` instance is fed HTML data and calls handler functions when tags The :class:`.HTMLParser` class is instantiated without arguments.
begin and end. The :class:`HTMLParser` class is meant to be overridden by the
user to provide a desired behavior.
Unlike the parser in :mod:`htmllib`, this parser does not check that end tags Unlike the parser in :mod:`htmllib`, this parser does not check that end tags
match start tags or call the end-tag handler for elements which are closed match start tags or call the end-tag handler for elements which are closed
...@@ -42,22 +43,59 @@ in :mod:`sgmllib`. ...@@ -42,22 +43,59 @@ in :mod:`sgmllib`.
An exception is defined as well: An exception is defined as well:
.. exception:: HTMLParseError .. exception:: HTMLParseError
Exception raised by the :class:`HTMLParser` class when it encounters an error :class:`.HTMLParser` is able to handle broken markup, but in some cases it
while parsing. This exception provides three attributes: :attr:`msg` is a brief might raise this exception when it encounters an error while parsing.
message explaining the error, :attr:`lineno` is the number of the line on which This exception provides three attributes: :attr:`msg` is a brief
the broken construct was detected, and :attr:`offset` is the number of message explaining the error, :attr:`lineno` is the number of the line on
which the broken construct was detected, and :attr:`offset` is the number of
characters into the line at which the construct starts. characters into the line at which the construct starts.
:class:`HTMLParser` instances have the following methods:
Example HTML Parser Application
-------------------------------
.. method:: HTMLParser.reset() 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 HTMLParser import HTMLParser
# create a subclass and override the handler methods
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
# instantiate the parser and fed it some HTML
parser = MyHTMLParser()
parser.feed('<html><head><title>Test</title></head>'
'<body><h1>Parse me!</h1></body></html>')
The output will then be::
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
Reset the instance. Loses all unprocessed data. This is called implicitly at
instantiation time. :class:`.HTMLParser` Methods
----------------------------
:class:`.HTMLParser` instances have the following methods:
.. method:: HTMLParser.feed(data) .. method:: HTMLParser.feed(data)
...@@ -73,7 +111,13 @@ An exception is defined as well: ...@@ -73,7 +111,13 @@ An exception is defined as well:
Force processing of all buffered data as if it were followed by an end-of-file 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 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 processing at the end of the input, but the redefined version should always call
the :class:`HTMLParser` base class method :meth:`close`. 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() .. method:: HTMLParser.getpos()
...@@ -89,22 +133,34 @@ An exception is defined as well: ...@@ -89,22 +133,34 @@ An exception is defined as well:
attributes can be preserved, etc.). 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) .. method:: HTMLParser.handle_starttag(tag, attrs)
This method is called to handle the start of a tag. It is intended to be This method is called to handle the start of a tag (e.g. ``<div id="main">``).
overridden by a derived class; the base class implementation does nothing.
The *tag* argument is the name of the tag converted to lower case. The *attrs* 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 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, 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 and quotes in the *value* have been removed, and character and entity references
have been replaced. For instance, for the tag ``<A have been replaced.
HREF="http://www.cwi.nl/">``, this method would be called as
``handle_starttag('a', [('href', 'http://www.cwi.nl/')])``. For instance, for the tag ``<A HREF="http://www.cwi.nl/">``, this method
would be called as ``handle_starttag('a', [('href', 'http://www.cwi.nl/')])``.
.. versionchanged:: 2.6 .. versionchanged:: 2.6
All entity references from :mod:`htmlentitydefs` are now replaced in the attribute All entity references from :mod:`htmlentitydefs` are now replaced in the
values. 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) .. method:: HTMLParser.handle_startendtag(tag, attrs)
...@@ -115,94 +171,175 @@ An exception is defined as well: ...@@ -115,94 +171,175 @@ An exception is defined as well:
implementation simply calls :meth:`handle_starttag` and :meth:`handle_endtag`. implementation simply calls :meth:`handle_starttag` and :meth:`handle_endtag`.
.. method:: HTMLParser.handle_endtag(tag)
This method is called to handle the end tag of an element. It is intended to be
overridden by a derived class; the base class implementation does nothing. The
*tag* argument is the name of the tag converted to lower case.
.. method:: HTMLParser.handle_data(data) .. method:: HTMLParser.handle_data(data)
This method is called to process arbitrary data (e.g. the content of This method is called to process arbitrary data (e.g. text nodes and the
``<script>...</script>`` and ``<style>...</style>``). It is intended to be content of ``<script>...</script>`` and ``<style>...</style>``).
overridden by a derived class; the base class implementation does nothing.
.. method:: HTMLParser.handle_charref(name) .. method:: HTMLParser.handle_entityref(name)
This method is called to process a character reference of the form ``&#ref;``. This method is called to process a named character reference of the form
It is intended to be overridden by a derived class; the base class ``&name;`` (e.g. ``&gt;``), where *name* is a general entity reference
implementation does nothing. (e.g. ``'gt'``).
.. method:: HTMLParser.handle_entityref(name) .. method:: HTMLParser.handle_charref(name)
This method is called to process a general entity reference of the form This method is called to process decimal and hexadecimal numeric character
``&name;`` where *name* is an general entity reference. It is intended to be references of the form ``&#NNN;`` and ``&#xNNN;``. For example, the decimal
overridden by a derived class; the base class implementation does nothing. equivalent for ``&gt;`` is ``&#62;``, whereas the hexadecimal is ``&#x3E;``;
in this case the method will receive ``'62'`` or ``'x3E'``.
.. method:: HTMLParser.handle_comment(data) .. method:: HTMLParser.handle_comment(data)
This method is called when a comment is encountered. The *comment* argument is This method is called when a comment is encountered (e.g. ``<!--comment-->``).
a string containing the text between the ``--`` and ``--`` delimiters, but not
the delimiters themselves. For example, the comment ``<!--text-->`` will cause
this method to be called with the argument ``'text'``. It is intended to be
overridden by a derived class; the base class implementation does nothing.
For example, the comment ``<!-- comment -->`` will cause this method to be
called with the argument ``' comment '``.
.. method:: HTMLParser.handle_decl(decl) 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]>IE-specific content<![endif]'``.
Method called when an SGML ``doctype`` declaration is read by the parser.
The *decl* parameter will be the entire contents of the declaration inside
the ``<!...>`` markup. It is intended to be overridden by a derived class;
the base class implementation does nothing.
.. method:: HTMLParser.handle_decl(decl)
.. method:: HTMLParser.unknown_decl(data) This method is called to handle an HTML doctype declaration (e.g.
``<!DOCTYPE html>``).
Method called when an unrecognized SGML declaration is read by the parser. The *decl* parameter will be the entire contents of the declaration inside
The *data* parameter will be the entire contents of the declaration inside the ``<!...>`` markup (e.g. ``'DOCTYPE html'``).
the ``<!...>`` markup. It is sometimes useful to be overridden by a
derived class; the base class implementation throws an :exc:`HTMLParseError`.
.. method:: HTMLParser.handle_pi(data) .. method:: HTMLParser.handle_pi(data)
Method called when a processing instruction is encountered. The *data* This method is called when a processing instruction is encountered. The *data*
parameter will contain the entire processing instruction. For example, for the parameter will contain the entire processing instruction. For example, for the
processing instruction ``<?proc color='red'>``, this method would be called as 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 ``handle_pi("proc color='red'")``.
class; the base class implementation does nothing.
.. note:: .. note::
The :class:`HTMLParser` class uses the SGML syntactic rules for processing The :class:`.HTMLParser` class uses the SGML syntactic rules for processing
instructions. An XHTML processing instruction using the trailing ``'?'`` will instructions. An XHTML processing instruction using the trailing ``'?'`` will
cause the ``'?'`` to be included in *data*. cause the ``'?'`` to be included in *data*.
.. _htmlparser-example: .. method:: HTMLParser.unknown_decl(data)
Example HTML Parser Application 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.
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 .. _htmlparser-examples:
as they are encountered::
Examples
--------
The following class implements a parser that will be used to illustrate more
examples::
from HTMLParser import HTMLParser from HTMLParser import HTMLParser
from htmlentitydefs import name2codepoint
class MyHTMLParser(HTMLParser): class MyHTMLParser(HTMLParser):
def handle_starttag(self, tag, attrs): def handle_starttag(self, tag, attrs):
print "Encountered a start tag:", tag print "Start tag:", tag
for attr in attrs:
print " attr:", attr
def handle_endtag(self, tag): def handle_endtag(self, tag):
print "Encountered an end tag:", tag print "End tag :", tag
def handle_data(self, data): def handle_data(self, data):
print "Encountered some data:", data print "Data :", data
def handle_comment(self, data):
print "Comment :", data
def handle_entityref(self, name):
c = unichr(name2codepoint[name])
print "Named ent:", c
def handle_charref(self, name):
if name.startswith('x'):
c = unichr(int(name[1:], 16))
else:
c = unichr(int(name))
print "Num ent :", c
def handle_decl(self, data):
print "Decl :", data
parser = MyHTMLParser() parser = MyHTMLParser()
parser.feed('<html><head><title>Test</title></head>'
'<body><h1>Parse me!</h1></body></html>') 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::
>>> 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
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