Doc/library/xmllib.rst

:mod:`xmllib` --- A parser for XML documents
============================================

.. module:: xmllib
   :synopsis: A parser for XML documents.
.. moduleauthor:: Sjoerd Mullender <Sjoerd.Mullender@cwi.nl>
.. sectionauthor:: Sjoerd Mullender <Sjoerd.Mullender@cwi.nl>


.. index::
   single: XML
   single: Extensible Markup Language

.. deprecated:: 2.0
   Use :mod:`xml.sax` instead.  The newer XML package includes full support for XML
   1.0.

.. versionchanged:: 1.5.2
   Added namespace support.

This module defines a class :class:`XMLParser` which serves as the basis  for
parsing text files formatted in XML (Extensible Markup Language).


.. class:: XMLParser()

   The :class:`XMLParser` class must be instantiated without arguments. [#]_

This class provides the following interface methods and instance variables:


.. attribute:: XMLParser.attributes

   A mapping of element names to mappings.  The latter mapping maps attribute names
   that are valid for the element to the default value of  the attribute, or if
   there is no default to ``None``.  The default value is the empty dictionary.
   This variable is meant to be overridden, not extended since the default is
   shared by all instances of :class:`XMLParser`.


.. attribute:: XMLParser.elements

   A mapping of element names to tuples.  The tuples contain a function for
   handling the start and end tag respectively of the element, or ``None`` if the
   method :meth:`unknown_starttag` or :meth:`unknown_endtag` is to be called.  The
   default value is the empty dictionary.  This variable is meant to be overridden,
   not extended since the default is shared by all instances of :class:`XMLParser`.


.. attribute:: XMLParser.entitydefs

   A mapping of entitynames to their values.  The default value contains
   definitions for ``'lt'``, ``'gt'``, ``'amp'``, ``'quot'``,  and ``'apos'``.


.. method:: XMLParser.reset()

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


.. method:: XMLParser.setnomoretags()

   Stop processing tags.  Treat all following input as literal input (CDATA).


.. method:: XMLParser.setliteral()

   Enter literal mode (CDATA mode).  This mode is automatically exited when the
   close tag matching the last unclosed open tag is encountered.


.. method:: XMLParser.feed(data)

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


.. method:: XMLParser.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
   :meth:`close`.


.. method:: XMLParser.translate_references(data)

   Translate all entity and character references in *data* and return the
   translated string.


.. method:: XMLParser.getnamespace()

   Return a mapping of namespace abbreviations to namespace URIs that are currently
   in effect.


.. method:: XMLParser.handle_xml(encoding, standalone)

   This method is called when the ``<?xml ...?>`` tag is processed. The arguments
   are the values of the encoding and standalone attributes  in the tag.  Both
   encoding and standalone are optional.  The values passed to :meth:`handle_xml`
   default to ``None`` and the string ``'no'`` respectively.


.. method:: XMLParser.handle_doctype(tag, pubid, syslit, data)

   .. index::
      single: DOCTYPE declaration
      single: Formal Public Identifier

   This method is called when the ``<!DOCTYPE...>`` declaration is processed.  The
   arguments are the tag name of the root element, the Formal Public Identifier (or
   ``None`` if not specified), the system identifier, and the uninterpreted
   contents of the internal DTD subset as a string (or ``None`` if not present).


.. method:: XMLParser.handle_starttag(tag, method, attributes)

   This method is called to handle start tags for which a start tag handler is
   defined in the instance variable :attr:`elements`.  The *tag* argument is the
   name of the tag, and the *method* argument is the function (method) which should
   be used to support semantic interpretation of the start tag.  The *attributes*
   argument is a dictionary of attributes, the key being the *name* and the value
   being the *value* of the attribute found inside the tag's ``<>`` brackets.
   Character and entity references in the *value* have been interpreted.  For
   instance, for the start tag ``<A HREF="http://www.cwi.nl/">``, this method would
   be called as ``handle_starttag('A', self.elements['A'][0], {'HREF':
   'http://www.cwi.nl/'})``.  The base implementation simply calls *method* with
   *attributes* as the only argument.


.. method:: XMLParser.handle_endtag(tag, method)

   This method is called to handle endtags for which an end tag handler is defined
   in the instance variable :attr:`elements`.  The *tag* argument is the name of
   the tag, and the *method* argument is the function (method) which should be used
   to support semantic interpretation of the end tag.  For instance, for the endtag
   ``</A>``, this method would be called as ``handle_endtag('A',
   self.elements['A'][1])``.  The base implementation simply calls *method*.


.. method:: XMLParser.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.


.. method:: XMLParser.handle_charref(ref)

   This method is called to process a character reference of the form ``&#ref;``.
   *ref* can either be a decimal number, or a hexadecimal number when preceded by
   an ``'x'``. In the base implementation, *ref* must be a number in the range
   0-255.  It translates the character to ASCII and calls the method
   :meth:`handle_data` with the character as argument.  If *ref* is invalid or out
   of range, the method ``unknown_charref(ref)`` is called to handle the error.  A
   subclass must override this method to provide support for character references
   outside of the ASCII range.


.. method:: XMLParser.handle_comment(comment)

   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'``.  The default method
   does nothing.


.. method:: XMLParser.handle_cdata(data)

   This method is called when a CDATA element is encountered.  The *data* argument
   is a string containing the text between the ``<![CDATA[`` and ``]]>``
   delimiters, but not the delimiters themselves.  For example, the entity
   ``<![CDATA[text]]>`` will cause this method to be called with the argument
   ``'text'``.  The default method does nothing, and is intended to be overridden.


.. method:: XMLParser.handle_proc(name, data)

   This method is called when a processing instruction (PI) is encountered.  The
   *name* is the PI target, and the *data* argument is a string containing the text
   between the PI target and the closing delimiter, but not the delimiter itself.
   For example, the instruction ``<?XML text?>`` will cause this method to be
   called with the arguments ``'XML'`` and ``'text'``.  The default method does
   nothing.  Note that if a document starts with ``<?xml ..?>``, :meth:`handle_xml`
   is called to handle it.


.. method:: XMLParser.handle_special(data)

   .. index:: single: ENTITY declaration

   This method is called when a declaration is encountered.  The *data* argument is
   a string containing the text between the ``<!`` and ``>`` delimiters, but not
   the delimiters themselves.  For example, the entity declaration ``<!ENTITY
   text>`` will cause this method to be called with the argument ``'ENTITY text'``.
   The default method does nothing.  Note that ``<!DOCTYPE ...>`` is handled
   separately if it is located at the start of the document.


.. method:: XMLParser.syntax_error(message)

   This method is called when a syntax error is encountered.  The *message* is a
   description of what was wrong.  The default method  raises a :exc:`RuntimeError`
   exception.  If this method is overridden, it is permissible for it to return.
   This method is only called when the error can be recovered from.  Unrecoverable
   errors raise a :exc:`RuntimeError` without first calling :meth:`syntax_error`.


.. method:: XMLParser.unknown_starttag(tag, attributes)

   This method is called to process an unknown start tag.  It is intended to be
   overridden by a derived class; the base class implementation does nothing.


.. method:: XMLParser.unknown_endtag(tag)

   This method is called to process an unknown end tag.  It is intended to be
   overridden by a derived class; the base class implementation does nothing.


.. method:: XMLParser.unknown_charref(ref)

   This method is called to process unresolvable numeric character references.  It
   is intended to be overridden by a derived class; the base class implementation
   does nothing.


.. method:: XMLParser.unknown_entityref(ref)

   This method is called to process an unknown entity reference.  It is intended to
   be overridden by a derived class; the base class implementation calls
   :meth:`syntax_error` to signal an error.


.. seealso::

   `Extensible Markup Language (XML) 1.0 <http://www.w3.org/TR/REC-xml>`_
      The XML specification, published by the World Wide Web Consortium (W3C), defines
      the syntax and processor requirements for XML.  References to additional
      material on XML, including translations of the specification, are available at
      http://www.w3.org/XML/.

   `Python and XML Processing <http://www.python.org/topics/xml/>`_
      The Python XML Topic Guide provides a great deal of information on using XML
      from Python and links to other sources of information on XML.

   `SIG for XML Processing in Python <http://www.python.org/sigs/xml-sig/>`_
      The Python XML Special Interest Group is developing substantial support for
      processing XML from Python.


.. _xml-namespace:

XML Namespaces
--------------

.. index:: pair: XML; namespaces

This module has support for XML namespaces as defined in the XML Namespaces
proposed recommendation.

Tag and attribute names that are defined in an XML namespace are handled as if
the name of the tag or element consisted of the namespace (the URL that defines
the namespace) followed by a space and the name of the tag or attribute.  For
instance, the tag ``<html xmlns='http://www.w3.org/TR/REC-html40'>`` is treated
as if  the tag name was ``'http://www.w3.org/TR/REC-html40 html'``, and the tag
``<html:a href='http://frob.com'>`` inside the above mentioned element is
treated as if the tag name were ``'http://www.w3.org/TR/REC-html40 a'`` and the
attribute name as if it were ``'http://www.w3.org/TR/REC-html40 href'``.

An older draft of the XML Namespaces proposal is also recognized, but triggers a
warning.


.. seealso::

   `Namespaces in XML <http://www.w3.org/TR/REC-xml-names/>`_
      This World Wide Web Consortium recommendation describes the proper syntax and
      processing requirements for namespaces in XML.

.. rubric:: Footnotes

.. [#] Actually, a number of keyword arguments are recognized which influence the
   parser to accept certain non-standard constructs.  The following keyword
   arguments are currently recognized.  The defaults for all of these is ``0``
   (false) except for the last one for which the default is ``1`` (true).
   *accept_unquoted_attributes* (accept certain attribute values without requiring
   quotes), *accept_missing_endtag_name* (accept end tags that look like ``</>``),
   *map_case* (map upper case to lower case in tags and attributes), *accept_utf8*
   (allow UTF-8 characters in input; this is required according to the XML
   standard, but Python does not as yet deal properly with these characters, so
   this is not the default), *translate_attribute_references* (don't attempt to
   translate character and entity references in attribute values).