Doc/library/xml.dom.minidom.rst

:mod:`xml.dom.minidom` --- Lightweight DOM implementation
=========================================================

.. module:: xml.dom.minidom
   :synopsis: Lightweight Document Object Model (DOM) implementation.
.. moduleauthor:: Paul Prescod <paul@prescod.net>
.. sectionauthor:: Paul Prescod <paul@prescod.net>
.. sectionauthor:: Martin v. Löwis <martin@v.loewis.de>


:mod:`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
:mod:`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 :func:`parse` function can take either a filename or an open file object.


.. function:: parse(filename_or_file, parser=None, bufsize=None)

   Return a :class:`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 :func:`parseString` function
instead:


.. function:: parseString(string, parser=None)

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

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

What the :func:`parse` and :func:`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 :class:`Document` by calling a method on a "DOM
Implementation" object.  You can get this object either by calling the
:func:`getDOMImplementation` function in the :mod:`xml.dom` package or the
:mod:`xml.dom.minidom` module. Using the implementation from the
:mod:`xml.dom.minidom` module will always return a :class:`Document` instance
from the minidom implementation, while the version from :mod:`xml.dom` may
provide an alternate implementation (this is likely if you have the `PyXML
package <http://pyxml.sourceforge.net/>`_ installed).  Once you have a
:class:`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
:attr:`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 tree, you may optionally call the
:meth:`unlink` method to encourage early cleanup of the now-unneeded
objects.  :meth:`unlink` is a :mod:`xml.dom.minidom`\ -specific
extension to the DOM API that renders the node and its descendants are
essentially useless.  Otherwise, Python's garbage collector will
eventually take care of the objects in the tree.

.. seealso::

   `Document Object Model (DOM) Level 1 Specification <http://www.w3.org/TR/REC-DOM-Level-1/>`_
      The W3C recommendation for the DOM supported by :mod:`xml.dom.minidom`.


.. _minidom-objects:

DOM Objects
-----------

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


.. method:: 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 :class:`Document` object, but may be called on child nodes
   to discard children of that node.

   You can avoid calling this method explicitly by using the :keyword:`with`
   statement. The following code will automatically unlink *dom* when the
   :keyword:`with` block is exited::

      with xml.dom.minidom.parse(datasource) as dom:
          ... # Work with dom.


.. method:: Node.writexml(writer, indent="", addindent="", newl="", encoding="")

   Write XML to the writer object.  The writer should have a :meth:`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 :class:`Document` node, an additional keyword argument *encoding* can be
   used to specify the encoding field of the XML header.


.. method:: Node.toxml(encoding=None)

   Return a string or byte string containing the XML represented by
   the DOM node.

   With an explicit *encoding* [1]_ argument, the result is a byte
   string in the specified encoding.  It is recommended that you
   always specify an encoding; you may use any encoding you like, but
   an argument of "utf-8" is the most common choice, avoiding
   :exc:`UnicodeError` exceptions in case of unrepresentable text
   data.

   With no *encoding* argument, the result is a Unicode string, and the
   XML declaration in the resulting string does not specify an
   encoding. Encoding this string in an encoding other than UTF-8 is
   likely incorrect, since UTF-8 is the default encoding of XML.

.. method:: 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``.

   The *encoding* argument behaves like the corresponding argument of
   :meth:`toxml`.


.. _dom-example:

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.

.. literalinclude:: ../includes/minidom-example.py


.. _minidom-and-dom:

minidom and the DOM standard
----------------------------

The :mod:`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 :class:`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 :keyword:`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 :meth:`_get_foo` and :meth:`_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. :mod:`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 :mod:`xml.dom.minidom`.
  Instead, :mod:`xml.dom.minidom` uses standard Python exceptions such as
  :exc:`TypeError` and :exc:`AttributeError`.

* :class:`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 :mod:`xml.dom.minidom`:

* :class:`DOMTimeStamp`

* :class:`DocumentType`

* :class:`DOMImplementation`

* :class:`CharacterData`

* :class:`CDATASection`

* :class:`Notation`

* :class:`Entity`

* :class:`EntityReference`

* :class:`DocumentFragment`

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

.. rubric:: Footnotes

.. [#] The encoding name included in the XML output should conform to
   the appropriate standards. For example, "UTF-8" is valid, but
   "UTF8" is not valid in an XML document's declaration, even though
   Python accepts it as an encoding name.
   See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
   and http://www.iana.org/assignments/character-sets .