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