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250 lines
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ReStructuredText
250 lines
9.8 KiB
ReStructuredText
:mod:`xml.dom.minidom` --- Lightweight DOM implementation
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=========================================================
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.. module:: xml.dom.minidom
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:synopsis: Lightweight Document Object Model (DOM) implementation.
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.. moduleauthor:: Paul Prescod <paul@prescod.net>
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.. sectionauthor:: Paul Prescod <paul@prescod.net>
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.. sectionauthor:: Martin v. Löwis <martin@v.loewis.de>
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**Source code:** :source:`Lib/xml/dom/minidom.py`
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--------------
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:mod:`xml.dom.minidom` is a light-weight implementation of the Document Object
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Model interface. It is intended to be simpler than the full DOM and also
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significantly smaller.
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DOM applications typically start by parsing some XML into a DOM. With
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:mod:`xml.dom.minidom`, this is done through the parse functions::
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from xml.dom.minidom import parse, parseString
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dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name
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datasource = open('c:\\temp\\mydata.xml')
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dom2 = parse(datasource) # parse an open file
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dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')
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The :func:`parse` function can take either a filename or an open file object.
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.. function:: parse(filename_or_file, parser=None, bufsize=None)
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Return a :class:`Document` from the given input. *filename_or_file* may be
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either a file name, or a file-like object. *parser*, if given, must be a SAX2
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parser object. This function will change the document handler of the parser and
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activate namespace support; other parser configuration (like setting an entity
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resolver) must have been done in advance.
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If you have XML in a string, you can use the :func:`parseString` function
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instead:
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.. function:: parseString(string, parser=None)
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Return a :class:`Document` that represents the *string*. This method creates a
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:class:`StringIO` object for the string and passes that on to :func:`parse`.
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Both functions return a :class:`Document` object representing the content of the
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document.
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What the :func:`parse` and :func:`parseString` functions do is connect an XML
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parser with a "DOM builder" that can accept parse events from any SAX parser and
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convert them into a DOM tree. The name of the functions are perhaps misleading,
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but are easy to grasp when learning the interfaces. The parsing of the document
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will be completed before these functions return; it's simply that these
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functions do not provide a parser implementation themselves.
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You can also create a :class:`Document` by calling a method on a "DOM
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Implementation" object. You can get this object either by calling the
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:func:`getDOMImplementation` function in the :mod:`xml.dom` package or the
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:mod:`xml.dom.minidom` module. Once you have a :class:`Document`, you
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can add child nodes to it to populate the DOM::
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from xml.dom.minidom import getDOMImplementation
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impl = getDOMImplementation()
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newdoc = impl.createDocument(None, "some_tag", None)
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top_element = newdoc.documentElement
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text = newdoc.createTextNode('Some textual content.')
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top_element.appendChild(text)
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Once you have a DOM document object, you can access the parts of your XML
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document through its properties and methods. These properties are defined in
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the DOM specification. The main property of the document object is the
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:attr:`documentElement` property. It gives you the main element in the XML
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document: the one that holds all others. Here is an example program::
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dom3 = parseString("<myxml>Some data</myxml>")
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assert dom3.documentElement.tagName == "myxml"
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When you are finished with a DOM tree, you may optionally call the
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:meth:`unlink` method to encourage early cleanup of the now-unneeded
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objects. :meth:`unlink` is a :mod:`xml.dom.minidom`\ -specific
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extension to the DOM API that renders the node and its descendants are
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essentially useless. Otherwise, Python's garbage collector will
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eventually take care of the objects in the tree.
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.. seealso::
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`Document Object Model (DOM) Level 1 Specification <http://www.w3.org/TR/REC-DOM-Level-1/>`_
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The W3C recommendation for the DOM supported by :mod:`xml.dom.minidom`.
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.. _minidom-objects:
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DOM Objects
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-----------
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The definition of the DOM API for Python is given as part of the :mod:`xml.dom`
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module documentation. This section lists the differences between the API and
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:mod:`xml.dom.minidom`.
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.. method:: Node.unlink()
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Break internal references within the DOM so that it will be garbage collected on
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versions of Python without cyclic GC. Even when cyclic GC is available, using
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this can make large amounts of memory available sooner, so calling this on DOM
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objects as soon as they are no longer needed is good practice. This only needs
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to be called on the :class:`Document` object, but may be called on child nodes
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to discard children of that node.
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You can avoid calling this method explicitly by using the :keyword:`with`
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statement. The following code will automatically unlink *dom* when the
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:keyword:`with` block is exited::
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with xml.dom.minidom.parse(datasource) as dom:
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... # Work with dom.
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.. method:: Node.writexml(writer, indent="", addindent="", newl="")
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Write XML to the writer object. The writer should have a :meth:`write` method
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which matches that of the file object interface. The *indent* parameter is the
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indentation of the current node. The *addindent* parameter is the incremental
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indentation to use for subnodes of the current one. The *newl* parameter
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specifies the string to use to terminate newlines.
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For the :class:`Document` node, an additional keyword argument *encoding* can
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be used to specify the encoding field of the XML header.
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.. method:: Node.toxml(encoding=None)
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Return a string or byte string containing the XML represented by
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the DOM node.
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With an explicit *encoding* [1]_ argument, the result is a byte
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string in the specified encoding. It is recommended that you
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always specify an encoding; you may use any encoding you like, but
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an argument of "utf-8" is the most common choice, avoiding
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:exc:`UnicodeError` exceptions in case of unrepresentable text
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data.
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With no *encoding* argument, the result is a Unicode string, and the
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XML declaration in the resulting string does not specify an
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encoding. Encoding this string in an encoding other than UTF-8 is
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likely incorrect, since UTF-8 is the default encoding of XML.
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.. method:: Node.toprettyxml(indent="", newl="", encoding="")
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Return a pretty-printed version of the document. *indent* specifies the
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indentation string and defaults to a tabulator; *newl* specifies the string
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emitted at the end of each line and defaults to ``\n``.
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The *encoding* argument behaves like the corresponding argument of
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:meth:`toxml`.
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.. _dom-example:
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DOM Example
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-----------
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This example program is a fairly realistic example of a simple program. In this
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particular case, we do not take much advantage of the flexibility of the DOM.
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.. literalinclude:: ../includes/minidom-example.py
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.. _minidom-and-dom:
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minidom and the DOM standard
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----------------------------
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The :mod:`xml.dom.minidom` module is essentially a DOM 1.0-compatible DOM with
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some DOM 2 features (primarily namespace features).
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Usage of the DOM interface in Python is straight-forward. The following mapping
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rules apply:
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* Interfaces are accessed through instance objects. Applications should not
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instantiate the classes themselves; they should use the creator functions
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available on the :class:`Document` object. Derived interfaces support all
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operations (and attributes) from the base interfaces, plus any new operations.
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* Operations are used as methods. Since the DOM uses only :keyword:`in`
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parameters, the arguments are passed in normal order (from left to right).
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There are no optional arguments. ``void`` operations return ``None``.
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* IDL attributes map to instance attributes. For compatibility with the OMG IDL
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language mapping for Python, an attribute ``foo`` can also be accessed through
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accessor methods :meth:`_get_foo` and :meth:`_set_foo`. ``readonly``
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attributes must not be changed; this is not enforced at runtime.
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* The types ``short int``, ``unsigned int``, ``unsigned long long``, and
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``boolean`` all map to Python integer objects.
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* The type ``DOMString`` maps to Python strings. :mod:`xml.dom.minidom` supports
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either bytes or strings, but will normally produce strings.
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Values of type ``DOMString`` may also be ``None`` where allowed to have the IDL
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``null`` value by the DOM specification from the W3C.
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* ``const`` declarations map to variables in their respective scope (e.g.
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``xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE``); they must not be changed.
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* ``DOMException`` is currently not supported in :mod:`xml.dom.minidom`.
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Instead, :mod:`xml.dom.minidom` uses standard Python exceptions such as
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:exc:`TypeError` and :exc:`AttributeError`.
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* :class:`NodeList` objects are implemented using Python's built-in list type.
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These objects provide the interface defined in the DOM specification, but with
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earlier versions of Python they do not support the official API. They are,
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however, much more "Pythonic" than the interface defined in the W3C
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recommendations.
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The following interfaces have no implementation in :mod:`xml.dom.minidom`:
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* :class:`DOMTimeStamp`
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* :class:`DocumentType`
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* :class:`DOMImplementation`
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* :class:`CharacterData`
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* :class:`CDATASection`
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* :class:`Notation`
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* :class:`Entity`
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* :class:`EntityReference`
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* :class:`DocumentFragment`
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Most of these reflect information in the XML document that is not of general
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utility to most DOM users.
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.. rubric:: Footnotes
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.. [#] The encoding name included in the XML output should conform to
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the appropriate standards. For example, "UTF-8" is valid, but
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"UTF8" is not valid in an XML document's declaration, even though
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Python accepts it as an encoding name.
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See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
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and http://www.iana.org/assignments/character-sets .
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