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pythonv / Doc / library / xml.dom.minidom.rst

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

Source code: :source:`Lib/xml/dom/minidom.py`


: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.

Note

The :mod:`xml.dom.minidom` module provides an implementation of the W3C-DOM, with an API similar to that in other programming languages. Users who are unfamiliar with the W3C-DOM interface or who would like to write less code for processing XML files should consider using the :mod:`xml.etree.ElementTree` module instead.

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.

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

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. 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.

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`.

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.

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`:

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

Footnotes

[1]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 .