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

  1
  2:mod:`xml.dom.minidom` --- Lightweight DOM implementation
  3=========================================================
  4
  5.. module:: xml.dom.minidom
  6   :synopsis: Lightweight Document Object Model (DOM) implementation.
  7.. moduleauthor:: Paul Prescod <paul@prescod.net>
  8.. sectionauthor:: Paul Prescod <paul@prescod.net>
  9.. sectionauthor:: Martin v. Lรถwis <martin@v.loewis.de>
 10
 11
 12.. versionadded:: 2.0
 13
 14:mod:`xml.dom.minidom` is a light-weight implementation of the Document Object
 15Model interface.  It is intended to be simpler than the full DOM and also
 16significantly smaller.
 17
 18DOM applications typically start by parsing some XML into a DOM.  With
 19:mod:`xml.dom.minidom`, this is done through the parse functions::
 20
 21   from xml.dom.minidom import parse, parseString
 22
 23   dom1 = parse('c:\\temp\\mydata.xml') # parse an XML file by name
 24
 25   datasource = open('c:\\temp\\mydata.xml')
 26   dom2 = parse(datasource)   # parse an open file
 27
 28   dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')
 29
 30The :func:`parse` function can take either a filename or an open file object.
 31
 32
 33.. function:: parse(filename_or_file[, parser[, bufsize]])
 34
 35   Return a :class:`Document` from the given input. *filename_or_file* may be
 36   either a file name, or a file-like object. *parser*, if given, must be a SAX2
 37   parser object. This function will change the document handler of the parser and
 38   activate namespace support; other parser configuration (like setting an entity
 39   resolver) must have been done in advance.
 40
 41If you have XML in a string, you can use the :func:`parseString` function
 42instead:
 43
 44
 45.. function:: parseString(string[, parser])
 46
 47   Return a :class:`Document` that represents the *string*. This method creates a
 48   :class:`StringIO` object for the string and passes that on to :func:`parse`.
 49
 50Both functions return a :class:`Document` object representing the content of the
 51document.
 52
 53What the :func:`parse` and :func:`parseString` functions do is connect an XML
 54parser with a "DOM builder" that can accept parse events from any SAX parser and
 55convert them into a DOM tree.  The name of the functions are perhaps misleading,
 56but are easy to grasp when learning the interfaces.  The parsing of the document
 57will be completed before these functions return; it's simply that these
 58functions do not provide a parser implementation themselves.
 59
 60You can also create a :class:`Document` by calling a method on a "DOM
 61Implementation" object.  You can get this object either by calling the
 62:func:`getDOMImplementation` function in the :mod:`xml.dom` package or the
 63:mod:`xml.dom.minidom` module. Using the implementation from the
 64:mod:`xml.dom.minidom` module will always return a :class:`Document` instance
 65from the minidom implementation, while the version from :mod:`xml.dom` may
 66provide an alternate implementation (this is likely if you have the `PyXML
 67package <http://pyxml.sourceforge.net/>`_ installed).  Once you have a
 68:class:`Document`, you can add child nodes to it to populate the DOM::
 69
 70   from xml.dom.minidom import getDOMImplementation
 71
 72   impl = getDOMImplementation()
 73
 74   newdoc = impl.createDocument(None, "some_tag", None)
 75   top_element = newdoc.documentElement
 76   text = newdoc.createTextNode('Some textual content.')
 77   top_element.appendChild(text)
 78
 79Once you have a DOM document object, you can access the parts of your XML
 80document through its properties and methods.  These properties are defined in
 81the DOM specification.  The main property of the document object is the
 82:attr:`documentElement` property.  It gives you the main element in the XML
 83document: the one that holds all others.  Here is an example program::
 84
 85   dom3 = parseString("<myxml>Some data</myxml>")
 86   assert dom3.documentElement.tagName == "myxml"
 87
 88When you are finished with a DOM, you should clean it up.  This is necessary
 89because some versions of Python do not support garbage collection of objects
 90that refer to each other in a cycle.  Until this restriction is removed from all
 91versions of Python, it is safest to write your code as if cycles would not be
 92cleaned up.
 93
 94The way to clean up a DOM is to call its :meth:`unlink` method::
 95
 96   dom1.unlink()
 97   dom2.unlink()
 98   dom3.unlink()
 99
100:meth:`unlink` is a :mod:`xml.dom.minidom`\ -specific extension to the DOM API.
101After calling :meth:`unlink` on a node, the node and its descendants are
102essentially useless.
103
104
105.. seealso::
106
107   `Document Object Model (DOM) Level 1 Specification <http://www.w3.org/TR/REC-DOM-Level-1/>`_
108      The W3C recommendation for the DOM supported by :mod:`xml.dom.minidom`.
109
110
111.. _minidom-objects:
112
113DOM Objects
114-----------
115
116The definition of the DOM API for Python is given as part of the :mod:`xml.dom`
117module documentation.  This section lists the differences between the API and
118:mod:`xml.dom.minidom`.
119
120
121.. method:: Node.unlink()
122
123   Break internal references within the DOM so that it will be garbage collected on
124   versions of Python without cyclic GC.  Even when cyclic GC is available, using
125   this can make large amounts of memory available sooner, so calling this on DOM
126   objects as soon as they are no longer needed is good practice.  This only needs
127   to be called on the :class:`Document` object, but may be called on child nodes
128   to discard children of that node.
129
130
131.. method:: Node.writexml(writer[, indent=""[, addindent=""[, newl=""[, encoding=""]]]])
132
133   Write XML to the writer object.  The writer should have a :meth:`write` method
134   which matches that of the file object interface.  The *indent* parameter is the
135   indentation of the current node.  The *addindent* parameter is the incremental
136   indentation to use for subnodes of the current one.  The *newl* parameter
137   specifies the string to use to terminate newlines.
138
139   .. versionchanged:: 2.1
140      The optional keyword parameters *indent*, *addindent*, and *newl* were added to
141      support pretty output.
142
143   .. versionchanged:: 2.3
144      For the :class:`Document` node, an additional keyword argument
145      *encoding* can be used to specify the encoding field of the XML header.
146
147
148.. method:: Node.toxml([encoding])
149
150   Return the XML that the DOM represents as a string.
151
152   With no argument, the XML header does not specify an encoding, and the result is
153   Unicode string if the default encoding cannot represent all characters in the
154   document. Encoding this string in an encoding other than UTF-8 is likely
155   incorrect, since UTF-8 is the default encoding of XML.
156
157   With an explicit *encoding* [1]_ argument, the result is a byte string in the
158   specified encoding. It is recommended that this argument is always specified. To
159   avoid :exc:`UnicodeError` exceptions in case of unrepresentable text data, the
160   encoding argument should be specified as "utf-8".
161
162   .. versionchanged:: 2.3
163      the *encoding* argument was introduced; see :meth:`writexml`.
164
165
166.. method:: Node.toprettyxml([indent=""[, newl=""[, encoding=""]]])
167
168   Return a pretty-printed version of the document. *indent* specifies the
169   indentation string and defaults to a tabulator; *newl* specifies the string
170   emitted at the end of each line and defaults to ``\n``.
171
172   .. versionadded:: 2.1
173
174   .. versionchanged:: 2.3
175      the encoding argument was introduced; see :meth:`writexml`.
176
177The following standard DOM methods have special considerations with
178:mod:`xml.dom.minidom`:
179
180
181.. method:: Node.cloneNode(deep)
182
183   Although this method was present in the version of :mod:`xml.dom.minidom`
184   packaged with Python 2.0, it was seriously broken.  This has been corrected for
185   subsequent releases.
186
187
188.. _dom-example:
189
190DOM Example
191-----------
192
193This example program is a fairly realistic example of a simple program. In this
194particular case, we do not take much advantage of the flexibility of the DOM.
195
196.. literalinclude:: ../includes/minidom-example.py
197
198
199.. _minidom-and-dom:
200
201minidom and the DOM standard
202----------------------------
203
204The :mod:`xml.dom.minidom` module is essentially a DOM 1.0-compatible DOM with
205some DOM 2 features (primarily namespace features).
206
207Usage of the DOM interface in Python is straight-forward.  The following mapping
208rules apply:
209
210* Interfaces are accessed through instance objects. Applications should not
211  instantiate the classes themselves; they should use the creator functions
212  available on the :class:`Document` object. Derived interfaces support all
213  operations (and attributes) from the base interfaces, plus any new operations.
214
215* Operations are used as methods. Since the DOM uses only :keyword:`in`
216  parameters, the arguments are passed in normal order (from left to right).
217  There are no optional arguments. ``void`` operations return ``None``.
218
219* IDL attributes map to instance attributes. For compatibility with the OMG IDL
220  language mapping for Python, an attribute ``foo`` can also be accessed through
221  accessor methods :meth:`_get_foo` and :meth:`_set_foo`.  ``readonly``
222  attributes must not be changed; this is not enforced at runtime.
223
224* The types ``short int``, ``unsigned int``, ``unsigned long long``, and
225  ``boolean`` all map to Python integer objects.
226
227* The type ``DOMString`` maps to Python strings. :mod:`xml.dom.minidom` supports
228  either byte or Unicode strings, but will normally produce Unicode strings.
229  Values of type ``DOMString`` may also be ``None`` where allowed to have the IDL
230  ``null`` value by the DOM specification from the W3C.
231
232* ``const`` declarations map to variables in their respective scope (e.g.
233  ``xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE``); they must not be changed.
234
235* ``DOMException`` is currently not supported in :mod:`xml.dom.minidom`.
236  Instead, :mod:`xml.dom.minidom` uses standard Python exceptions such as
237  :exc:`TypeError` and :exc:`AttributeError`.
238
239* :class:`NodeList` objects are implemented using Python's built-in list type.
240  Starting with Python 2.2, these objects provide the interface defined in the DOM
241  specification, but with earlier versions of Python they do not support the
242  official API.  They are, however, much more "Pythonic" than the interface
243  defined in the W3C recommendations.
244
245The following interfaces have no implementation in :mod:`xml.dom.minidom`:
246
247* :class:`DOMTimeStamp`
248
249* :class:`DocumentType` (added in Python 2.1)
250
251* :class:`DOMImplementation` (added in Python 2.1)
252
253* :class:`CharacterData`
254
255* :class:`CDATASection`
256
257* :class:`Notation`
258
259* :class:`Entity`
260
261* :class:`EntityReference`
262
263* :class:`DocumentFragment`
264
265Most of these reflect information in the XML document that is not of general
266utility to most DOM users.
267
268.. rubric:: Footnotes
269
270.. [#] The encoding string included in XML output should conform to the
271   appropriate standards. For example, "UTF-8" is valid, but "UTF8" is
272   not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
273   and http://www.iana.org/assignments/character-sets .