
``html.parser`` --- Simple HTML and XHTML parser
************************************************

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

======================================================================

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

class class html.parser.HTMLParser(strict=True)

   Create a parser instance.  If *strict* is ``True`` (the default),
   invalid html results in ``HTMLParseError`` exceptions [1].  If
   *strict* is ``False``, the parser uses heuristics to make a best
   guess at the intention of any invalid html it encounters, similar
   to the way most browsers do.

   An ``HTMLParser`` instance is fed HTML data and calls handler
   functions when tags begin and end.  The ``HTMLParser`` class is
   meant to be overridden by the user to provide a 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.

   Changed in version 3.2: *strict* keyword added

An exception is defined as well:

exception exception html.parser.HTMLParseError

   Exception raised by the ``HTMLParser`` class when it encounters an
   error while parsing.  This exception provides three attributes:
   ``msg`` is a brief message explaining the error, ``lineno`` is the
   number of the line on which the broken construct was detected, and
   ``offset`` is the number of characters into the line at which the
   construct starts.

``HTMLParser`` instances have the following methods:

HTMLParser.reset()

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

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 ``close()`` is called.

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 ``HTMLParser`` base class
   method ``close()``.

HTMLParser.getpos()

   Return current line number and offset.

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.).

HTMLParser.handle_starttag(tag, attrs)

   This method is called to handle the start of a tag.  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.
   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="http://www.cwi.nl/">``, this method would be called as
   ``handle_starttag('a', [('href', 'http://www.cwi.nl/')])``.

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

HTMLParser.handle_startendtag(tag, attrs)

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

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.

HTMLParser.handle_data(data)

   This method is called to process arbitrary data.  It is intended to
   be overridden by a derived class; the base class implementation
   does nothing.

HTMLParser.handle_charref(name)

   This method is called to process a character reference of the form
   ``&#ref;``. It is intended to be overridden by a derived class; the
   base class implementation does nothing.

HTMLParser.handle_entityref(name)

   This method is called to process a general entity reference of the
   form ``&name;`` where *name* is an general entity reference.  It is
   intended to be overridden by a derived class; the base class
   implementation does nothing.

HTMLParser.handle_comment(data)

   This method is called when a comment is encountered.  The *comment*
   argument is 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.

HTMLParser.handle_decl(decl)

   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.

HTMLParser.unknown_decl(data)

   Method called when an unrecognized SGML 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
   raises an ``HTMLParseError``.

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 ``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*.


Example HTML Parser Application
===============================

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

   >>> from html.parser import HTMLParser
   >>>
   >>> class MyHTMLParser(HTMLParser):
   ...     def handle_starttag(self, tag, attrs):
   ...         print("Encountered a {} start tag".format(tag))
   ...     def handle_endtag(self, tag):
   ...         print("Encountered a {} end tag".format(tag))
   ...
   >>> page = """<html><h1>Title</h1><p>I'm a paragraph!</p></html>"""
   >>>
   >>> myparser = MyHTMLParser()
   >>> myparser.feed(page)
   Encountered a html start tag
   Encountered a h1 start tag
   Encountered a h1 end tag
   Encountered a p start tag
   Encountered a p end tag
   Encountered a html end tag

-[ Footnotes ]-

[1] For backward compatibility reasons *strict* mode does not raise
    exceptions for all non-compliant HTML.  That is, some invalid HTML
    is tolerated even in *strict* mode.
