
``xml.dom.minidom`` --- Lightweight DOM implementation
******************************************************

``xml.dom.minidom`` is a light-weight implementation of the Document
Object Model interface.  It is intended to be simpler than the full
DOM and also significantly smaller.

DOM applications typically start by parsing some XML into a DOM.  With
``xml.dom.minidom``, this is done through the parse functions:

   from xml.dom.minidom import parse, parseString

   dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name

   datasource = open('c:\\temp\\mydata.xml')
   dom2 = parse(datasource)   # parse an open file

   dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')

The ``parse()`` function can take either a filename or an open file
object.

xml.dom.minidom.parse(filename_or_file, parser)

   Return a ``Document`` from the given input. *filename_or_file* may
   be either a file name, or a file-like object. *parser*, if given,
   must be a SAX2 parser object. This function will change the
   document handler of the parser and activate namespace support;
   other parser configuration (like setting an entity resolver) must
   have been done in advance.

If you have XML in a string, you can use the ``parseString()``
function instead:

xml.dom.minidom.parseString(string[, parser])

   Return a ``Document`` that represents the *string*. This method
   creates a ``StringIO`` object for the string and passes that on to
   ``parse()``.

Both functions return a ``Document`` object representing the content
of the document.

What the ``parse()`` and ``parseString()`` functions do is connect an
XML parser with a "DOM builder" that can accept parse events from any
SAX parser and convert them into a DOM tree.  The name of the
functions are perhaps misleading, but are easy to grasp when learning
the interfaces.  The parsing of the document will be completed before
these functions return; it's simply that these functions do not
provide a parser implementation themselves.

You can also create a ``Document`` by calling a method on a "DOM
Implementation" object.  You can get this object either by calling the
``getDOMImplementation()`` function in the ``xml.dom`` package or the
``xml.dom.minidom`` module. Using the implementation from the
``xml.dom.minidom`` module will always return a ``Document`` instance
from the minidom implementation, while the version from ``xml.dom``
may provide an alternate implementation (this is likely if you have
the PyXML package installed).  Once you have a ``Document``, you can
add child nodes to it to populate the DOM:

   from xml.dom.minidom import getDOMImplementation

   impl = getDOMImplementation()

   newdoc = impl.createDocument(None, "some_tag", None)
   top_element = newdoc.documentElement
   text = newdoc.createTextNode('Some textual content.')
   top_element.appendChild(text)

Once you have a DOM document object, you can access the parts of your
XML document through its properties and methods.  These properties are
defined in the DOM specification.  The main property of the document
object is the ``documentElement`` property.  It gives you the main
element in the XML document: the one that holds all others.  Here is
an example program:

   dom3 = parseString("<myxml>Some data</myxml>")
   assert dom3.documentElement.tagName == "myxml"

When you are finished with a DOM, you should clean it up.  This is
necessary because some versions of Python do not support garbage
collection of objects that refer to each other in a cycle.  Until this
restriction is removed from all versions of Python, it is safest to
write your code as if cycles would not be cleaned up.

The way to clean up a DOM is to call its ``unlink()`` method:

   dom1.unlink()
   dom2.unlink()
   dom3.unlink()

``unlink()`` is a ``xml.dom.minidom``-specific extension to the DOM
API. After calling ``unlink()`` on a node, the node and its
descendants are essentially useless.

See also:

   Document Object Model (DOM) Level 1 Specification
      The W3C recommendation for the DOM supported by
      ``xml.dom.minidom``.


DOM Objects
===========

The definition of the DOM API for Python is given as part of the
``xml.dom`` module documentation.  This section lists the differences
between the API and ``xml.dom.minidom``.

Node.unlink()

   Break internal references within the DOM so that it will be garbage
   collected on versions of Python without cyclic GC.  Even when
   cyclic GC is available, using this can make large amounts of memory
   available sooner, so calling this on DOM objects as soon as they
   are no longer needed is good practice.  This only needs to be
   called on the ``Document`` object, but may be called on child nodes
   to discard children of that node.

Node.writexml(writer[, indent=""[, addindent=""[, newl=""[, encoding=""]]]])

   Write XML to the writer object.  The writer should have a
   ``write()`` method which matches that of the file object interface.
   The *indent* parameter is the indentation of the current node.  The
   *addindent* parameter is the incremental indentation to use for
   subnodes of the current one.  The *newl* parameter specifies the
   string to use to terminate newlines.

   For the ``Document`` node, an additional keyword argument
   *encoding* can be used to specify the encoding field of the XML
   header.

Node.toxml([encoding])

   Return the XML that the DOM represents as a string.

   With no argument, the XML header does not specify an encoding, and
   the result is Unicode string if the default encoding cannot
   represent all characters in the document. Encoding this string in
   an encoding other than UTF-8 is likely incorrect, since UTF-8 is
   the default encoding of XML.

   With an explicit *encoding* [1] argument, the result is a byte
   string in the specified encoding. It is recommended that this
   argument is always specified. To avoid ``UnicodeError`` exceptions
   in case of unrepresentable text data, the encoding argument should
   be specified as "utf-8".

Node.toprettyxml([indent=""[, newl=""[, encoding=""]]])

   Return a pretty-printed version of the document. *indent* specifies
   the indentation string and defaults to a tabulator; *newl*
   specifies the string emitted at the end of each line and defaults
   to ``\n``.

   There's also an *encoding* argument; see ``toxml()``.


DOM Example
===========

This example program is a fairly realistic example of a simple
program. In this particular case, we do not take much advantage of the
flexibility of the DOM.

   import xml.dom.minidom

   document = """\
   <slideshow>
   <title>Demo slideshow</title>
   <slide><title>Slide title</title>
   <point>This is a demo</point>
   <point>Of a program for processing slides</point>
   </slide>

   <slide><title>Another demo slide</title>
   <point>It is important</point>
   <point>To have more than</point>
   <point>one slide</point>
   </slide>
   </slideshow>
   """

   dom = xml.dom.minidom.parseString(document)

   def getText(nodelist):
       rc = ""
       for node in nodelist:
           if node.nodeType == node.TEXT_NODE:
               rc = rc + node.data
       return rc

   def handleSlideshow(slideshow):
       print("<html>")
       handleSlideshowTitle(slideshow.getElementsByTagName("title")[0])
       slides = slideshow.getElementsByTagName("slide")
       handleToc(slides)
       handleSlides(slides)
       print("</html>")

   def handleSlides(slides):
       for slide in slides:
           handleSlide(slide)

   def handleSlide(slide):
       handleSlideTitle(slide.getElementsByTagName("title")[0])
       handlePoints(slide.getElementsByTagName("point"))

   def handleSlideshowTitle(title):
       print("<title>%s</title>" % getText(title.childNodes))

   def handleSlideTitle(title):
       print("<h2>%s</h2>" % getText(title.childNodes))

   def handlePoints(points):
       print("<ul>")
       for point in points:
           handlePoint(point)
       print("</ul>")

   def handlePoint(point):
       print("<li>%s</li>" % getText(point.childNodes))

   def handleToc(slides):
       for slide in slides:
           title = slide.getElementsByTagName("title")[0]
           print("<p>%s</p>" % getText(title.childNodes))

   handleSlideshow(dom)


minidom and the DOM standard
============================

The ``xml.dom.minidom`` module is essentially a DOM 1.0-compatible DOM
with some DOM 2 features (primarily namespace features).

Usage of the DOM interface in Python is straight-forward.  The
following mapping rules apply:

* Interfaces are accessed through instance objects. Applications
  should not instantiate the classes themselves; they should use the
  creator functions available on the ``Document`` object. Derived
  interfaces support all operations (and attributes) from the base
  interfaces, plus any new operations.

* Operations are used as methods. Since the DOM uses only ``in``
  parameters, the arguments are passed in normal order (from left to
  right). There are no optional arguments. ``void`` operations return
  ``None``.

* IDL attributes map to instance attributes. For compatibility with
  the OMG IDL language mapping for Python, an attribute ``foo`` can
  also be accessed through accessor methods ``_get_foo()`` and
  ``_set_foo()``.  ``readonly`` attributes must not be changed; this
  is not enforced at runtime.

* The types ``short int``, ``unsigned int``, ``unsigned long long``,
  and ``boolean`` all map to Python integer objects.

* The type ``DOMString`` maps to Python strings. ``xml.dom.minidom``
  supports either bytes or strings, but will normally produce strings.
  Values of type ``DOMString`` may also be ``None`` where allowed to
  have the IDL ``null`` value by the DOM specification from the W3C.

* ``const`` declarations map to variables in their respective scope
  (e.g. ``xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE``); they
  must not be changed.

* ``DOMException`` is currently not supported in ``xml.dom.minidom``.
  Instead, ``xml.dom.minidom`` uses standard Python exceptions such as
  ``TypeError`` and ``AttributeError``.

* ``NodeList`` objects are implemented using Python's built-in list
  type. These objects provide the interface defined in the DOM
  specification, but with earlier versions of Python they do not
  support the official API.  They are, however, much more "Pythonic"
  than the interface defined in the W3C recommendations.

The following interfaces have no implementation in
``xml.dom.minidom``:

* ``DOMTimeStamp``

* ``DocumentType``

* ``DOMImplementation``

* ``CharacterData``

* ``CDATASection``

* ``Notation``

* ``Entity``

* ``EntityReference``

* ``DocumentFragment``

Most of these reflect information in the XML document that is not of
general utility to most DOM users.

-[ Footnotes ]-

[1] The encoding string included in XML output should conform to the
    appropriate standards. For example, "UTF-8" is valid, but "UTF8"
    is not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-
    EncodingDecl and http://www.iana.org/assignments/character-sets .
