2 :mod:`xml.etree.ElementTree` --- The ElementTree XML API
3 ========================================================
5 .. module:: xml.etree.ElementTree
6 :synopsis: Implementation of the ElementTree API.
7 .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>
12 The Element type is a flexible container object, designed to store hierarchical
13 data structures in memory. The type can be described as a cross between a list
16 Each element has a number of properties associated with it:
18 * a tag which is a string identifying what kind of data this element represents
19 (the element type, in other words).
21 * a number of attributes, stored in a Python dictionary.
25 * an optional tail string.
27 * a number of child elements, stored in a Python sequence
29 To create an element instance, use the Element or SubElement factory functions.
31 The :class:`ElementTree` class can be used to wrap an element structure, and
32 convert it from and to XML.
34 A C implementation of this API is available as :mod:`xml.etree.cElementTree`.
36 See http://effbot.org/zone/element-index.htm for tutorials and links to other
37 docs. Fredrik Lundh's page is also the location of the development version of the
38 xml.etree.ElementTree.
40 .. _elementtree-functions:
46 .. function:: Comment([text])
48 Comment element factory. This factory function creates a special element that
49 will be serialized as an XML comment. The comment string can be either an 8-bit
50 ASCII string or a Unicode string. *text* is a string containing the comment
51 string. Returns an element instance representing a comment.
54 .. function:: dump(elem)
56 Writes an element tree or element structure to sys.stdout. This function should
57 be used for debugging only.
59 The exact output format is implementation dependent. In this version, it's
60 written as an ordinary XML file.
62 *elem* is an element tree or an individual element.
65 .. function:: Element(tag[, attrib][, **extra])
67 Element factory. This function returns an object implementing the standard
68 Element interface. The exact class or type of that object is implementation
69 dependent, but it will always be compatible with the _ElementInterface class in
72 The element name, attribute names, and attribute values can be either 8-bit
73 ASCII strings or Unicode strings. *tag* is the element name. *attrib* is an
74 optional dictionary, containing element attributes. *extra* contains additional
75 attributes, given as keyword arguments. Returns an element instance.
78 .. function:: fromstring(text)
80 Parses an XML section from a string constant. Same as XML. *text* is a string
81 containing XML data. Returns an Element instance.
84 .. function:: iselement(element)
86 Checks if an object appears to be a valid element object. *element* is an
87 element instance. Returns a true value if this is an element object.
90 .. function:: iterparse(source[, events])
92 Parses an XML section into an element tree incrementally, and reports what's
93 going on to the user. *source* is a filename or file object containing XML data.
94 *events* is a list of events to report back. If omitted, only "end" events are
95 reported. Returns an :term:`iterator` providing ``(event, elem)`` pairs.
99 :func:`iterparse` only guarantees that it has seen the ">"
100 character of a starting tag when it emits a "start" event, so the
101 attributes are defined, but the contents of the text and tail attributes
102 are undefined at that point. The same applies to the element children;
103 they may or may not be present.
105 If you need a fully populated element, look for "end" events instead.
108 .. function:: parse(source[, parser])
110 Parses an XML section into an element tree. *source* is a filename or file
111 object containing XML data. *parser* is an optional parser instance. If not
112 given, the standard XMLTreeBuilder parser is used. Returns an ElementTree
116 .. function:: ProcessingInstruction(target[, text])
118 PI element factory. This factory function creates a special element that will
119 be serialized as an XML processing instruction. *target* is a string containing
120 the PI target. *text* is a string containing the PI contents, if given. Returns
121 an element instance, representing a processing instruction.
124 .. function:: SubElement(parent, tag[, attrib[, **extra]])
126 Subelement factory. This function creates an element instance, and appends it
127 to an existing element.
129 The element name, attribute names, and attribute values can be either 8-bit
130 ASCII strings or Unicode strings. *parent* is the parent element. *tag* is the
131 subelement name. *attrib* is an optional dictionary, containing element
132 attributes. *extra* contains additional attributes, given as keyword arguments.
133 Returns an element instance.
136 .. function:: tostring(element[, encoding])
138 Generates a string representation of an XML element, including all subelements.
139 *element* is an Element instance. *encoding* is the output encoding (default is
140 US-ASCII). Returns an encoded string containing the XML data.
143 .. function:: XML(text)
145 Parses an XML section from a string constant. This function can be used to
146 embed "XML literals" in Python code. *text* is a string containing XML data.
147 Returns an Element instance.
150 .. function:: XMLID(text)
152 Parses an XML section from a string constant, and also returns a dictionary
153 which maps from element id:s to elements. *text* is a string containing XML
154 data. Returns a tuple containing an Element instance and a dictionary.
157 .. _elementtree-element-interface:
159 The Element Interface
160 ---------------------
162 Element objects returned by Element or SubElement have the following methods
166 .. attribute:: Element.tag
168 A string identifying what kind of data this element represents (the element
169 type, in other words).
172 .. attribute:: Element.text
174 The *text* attribute can be used to hold additional data associated with the
175 element. As the name implies this attribute is usually a string but may be any
176 application-specific object. If the element is created from an XML file the
177 attribute will contain any text found between the element tags.
180 .. attribute:: Element.tail
182 The *tail* attribute can be used to hold additional data associated with the
183 element. This attribute is usually a string but may be any application-specific
184 object. If the element is created from an XML file the attribute will contain
185 any text found after the element's end tag and before the next tag.
188 .. attribute:: Element.attrib
190 A dictionary containing the element's attributes. Note that while the *attrib*
191 value is always a real mutable Python dictionary, an ElementTree implementation
192 may choose to use another internal representation, and create the dictionary
193 only if someone asks for it. To take advantage of such implementations, use the
194 dictionary methods below whenever possible.
196 The following dictionary-like methods work on the element attributes.
199 .. method:: Element.clear()
201 Resets an element. This function removes all subelements, clears all
202 attributes, and sets the text and tail attributes to None.
205 .. method:: Element.get(key[, default=None])
207 Gets the element attribute named *key*.
209 Returns the attribute value, or *default* if the attribute was not found.
212 .. method:: Element.items()
214 Returns the element attributes as a sequence of (name, value) pairs. The
215 attributes are returned in an arbitrary order.
218 .. method:: Element.keys()
220 Returns the elements attribute names as a list. The names are returned in an
224 .. method:: Element.set(key, value)
226 Set the attribute *key* on the element to *value*.
228 The following methods work on the element's children (subelements).
231 .. method:: Element.append(subelement)
233 Adds the element *subelement* to the end of this elements internal list of
237 .. method:: Element.find(match)
239 Finds the first subelement matching *match*. *match* may be a tag name or path.
240 Returns an element instance or ``None``.
243 .. method:: Element.findall(match)
245 Finds all subelements matching *match*. *match* may be a tag name or path.
246 Returns an iterable yielding all matching elements in document order.
249 .. method:: Element.findtext(condition[, default=None])
251 Finds text for the first subelement matching *condition*. *condition* may be a
252 tag name or path. Returns the text content of the first matching element, or
253 *default* if no element was found. Note that if the matching element has no
254 text content an empty string is returned.
257 .. method:: Element.getchildren()
259 Returns all subelements. The elements are returned in document order.
262 .. method:: Element.getiterator([tag=None])
264 Creates a tree iterator with the current element as the root. The iterator
265 iterates over this element and all elements below it, in document (depth first)
266 order. If *tag* is not ``None`` or ``'*'``, only elements whose tag equals
267 *tag* are returned from the iterator.
270 .. method:: Element.insert(index, element)
272 Inserts a subelement at the given position in this element.
275 .. method:: Element.makeelement(tag, attrib)
277 Creates a new element object of the same type as this element. Do not call this
278 method, use the SubElement factory function instead.
281 .. method:: Element.remove(subelement)
283 Removes *subelement* from the element. Unlike the findXYZ methods this method
284 compares elements based on the instance identity, not on tag value or contents.
286 Element objects also support the following sequence type methods for working
287 with subelements: :meth:`__delitem__`, :meth:`__getitem__`, :meth:`__setitem__`,
290 Caution: Because Element objects do not define a :meth:`__nonzero__` method,
291 elements with no subelements will test as ``False``. ::
293 element = root.find('foo')
295 if not element: # careful!
296 print "element not found, or element has no subelements"
299 print "element not found"
302 .. _elementtree-elementtree-objects:
308 .. class:: ElementTree([element,] [file])
310 ElementTree wrapper class. This class represents an entire element hierarchy,
311 and adds some extra support for serialization to and from standard XML.
313 *element* is the root element. The tree is initialized with the contents of the
317 .. method:: _setroot(element)
319 Replaces the root element for this tree. This discards the current
320 contents of the tree, and replaces it with the given element. Use with
321 care. *element* is an element instance.
324 .. method:: find(path)
326 Finds the first toplevel element with given tag. Same as
327 getroot().find(path). *path* is the element to look for. Returns the
328 first matching element, or ``None`` if no element was found.
331 .. method:: findall(path)
333 Finds all toplevel elements with the given tag. Same as
334 getroot().findall(path). *path* is the element to look for. Returns a
335 list or :term:`iterator` containing all matching elements, in document
339 .. method:: findtext(path[, default])
341 Finds the element text for the first toplevel element with given tag.
342 Same as getroot().findtext(path). *path* is the toplevel element to look
343 for. *default* is the value to return if the element was not
344 found. Returns the text content of the first matching element, or the
345 default value no element was found. Note that if the element has is
346 found, but has no text content, this method returns an empty string.
349 .. method:: getiterator([tag])
351 Creates and returns a tree iterator for the root element. The iterator
352 loops over all elements in this tree, in section order. *tag* is the tag
353 to look for (default is to return all elements)
356 .. method:: getroot()
358 Returns the root element for this tree.
361 .. method:: parse(source[, parser])
363 Loads an external XML section into this element tree. *source* is a file
364 name or file object. *parser* is an optional parser instance. If not
365 given, the standard XMLTreeBuilder parser is used. Returns the section
369 .. method:: write(file[, encoding])
371 Writes the element tree to a file, as XML. *file* is a file name, or a
372 file object opened for writing. *encoding* [1]_ is the output encoding
373 (default is US-ASCII).
375 This is the XML file that is going to be manipulated::
379 <title>Example page</title>
382 <p>Moved to <a href="http://example.org/">example.org</a>
383 or <a href="http://example.com/">example.com</a>.</p>
387 Example of changing the attribute "target" of every link in first paragraph::
389 >>> from xml.etree.ElementTree import ElementTree
390 >>> tree = ElementTree()
391 >>> tree.parse("index.xhtml")
392 <Element html at b7d3f1ec>
393 >>> p = tree.find("body/p") # Finds first occurrence of tag p in body
395 <Element p at 8416e0c>
396 >>> links = p.getiterator("a") # Returns list of all links
398 [<Element a at b7d4f9ec>, <Element a at b7d4fb0c>]
399 >>> for i in links: # Iterates through all found links
400 ... i.attrib["target"] = "blank"
401 >>> tree.write("output.xhtml")
403 .. _elementtree-qname-objects:
409 .. class:: QName(text_or_uri[, tag])
411 QName wrapper. This can be used to wrap a QName attribute value, in order to
412 get proper namespace handling on output. *text_or_uri* is a string containing
413 the QName value, in the form {uri}local, or, if the tag argument is given, the
414 URI part of a QName. If *tag* is given, the first argument is interpreted as an
415 URI, and this argument is interpreted as a local name. :class:`QName` instances
419 .. _elementtree-treebuilder-objects:
425 .. class:: TreeBuilder([element_factory])
427 Generic element structure builder. This builder converts a sequence of start,
428 data, and end method calls to a well-formed element structure. You can use this
429 class to build an element structure using a custom XML parser, or a parser for
430 some other XML-like format. The *element_factory* is called to create new
431 Element instances when given.
436 Flushes the parser buffers, and returns the toplevel document
437 element. Returns an Element instance.
440 .. method:: data(data)
442 Adds text to the current element. *data* is a string. This should be
443 either an 8-bit string containing ASCII text, or a Unicode string.
448 Closes the current element. *tag* is the element name. Returns the closed
452 .. method:: start(tag, attrs)
454 Opens a new element. *tag* is the element name. *attrs* is a dictionary
455 containing element attributes. Returns the opened element.
458 .. _elementtree-xmltreebuilder-objects:
460 XMLTreeBuilder Objects
461 ----------------------
464 .. class:: XMLTreeBuilder([html,] [target])
466 Element structure builder for XML source data, based on the expat parser. *html*
467 are predefined HTML entities. This flag is not supported by the current
468 implementation. *target* is the target object. If omitted, the builder uses an
469 instance of the standard TreeBuilder class.
474 Finishes feeding data to the parser. Returns an element structure.
477 .. method:: doctype(name, pubid, system)
479 Handles a doctype declaration. *name* is the doctype name. *pubid* is the
480 public identifier. *system* is the system identifier.
483 .. method:: feed(data)
485 Feeds data to the parser. *data* is encoded data.
487 :meth:`XMLTreeBuilder.feed` calls *target*\'s :meth:`start` method
488 for each opening tag, its :meth:`end` method for each closing tag,
489 and data is processed by method :meth:`data`. :meth:`XMLTreeBuilder.close`
490 calls *target*\'s method :meth:`close`.
491 :class:`XMLTreeBuilder` can be used not only for building a tree structure.
492 This is an example of counting the maximum depth of an XML file::
494 >>> from xml.etree.ElementTree import XMLTreeBuilder
495 >>> class MaxDepth: # The target object of the parser
498 ... def start(self, tag, attrib): # Called for each opening tag.
500 ... if self.depth > self.maxDepth:
501 ... self.maxDepth = self.depth
502 ... def end(self, tag): # Called for each closing tag.
504 ... def data(self, data):
505 ... pass # We do not need to do anything with data.
506 ... def close(self): # Called when all data has been parsed.
507 ... return self.maxDepth
509 >>> target = MaxDepth()
510 >>> parser = XMLTreeBuilder(target=target)
522 >>> parser.feed(exampleXml)
527 .. rubric:: Footnotes
529 .. [#] The encoding string included in XML output should conform to the
530 appropriate standards. For example, "UTF-8" is valid, but "UTF8" is
531 not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
532 and http://www.iana.org/assignments/character-sets.