/Doc/library/xml.etree.elementtree.rst
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- :mod:`xml.etree.ElementTree` --- The ElementTree XML API
- ========================================================
- .. module:: xml.etree.ElementTree
- :synopsis: Implementation of the ElementTree API.
- .. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>
- .. versionadded:: 2.5
- The Element type is a flexible container object, designed to store hierarchical
- data structures in memory. The type can be described as a cross between a list
- and a dictionary.
- Each element has a number of properties associated with it:
- * a tag which is a string identifying what kind of data this element represents
- (the element type, in other words).
- * a number of attributes, stored in a Python dictionary.
- * a text string.
- * an optional tail string.
- * a number of child elements, stored in a Python sequence
- To create an element instance, use the Element or SubElement factory functions.
- The :class:`ElementTree` class can be used to wrap an element structure, and
- convert it from and to XML.
- A C implementation of this API is available as :mod:`xml.etree.cElementTree`.
- See http://effbot.org/zone/element-index.htm for tutorials and links to other
- docs. Fredrik Lundh's page is also the location of the development version of the
- xml.etree.ElementTree.
- .. _elementtree-functions:
- Functions
- ---------
- .. function:: Comment([text])
- Comment element factory. This factory function creates a special element that
- will be serialized as an XML comment. The comment string can be either an 8-bit
- ASCII string or a Unicode string. *text* is a string containing the comment
- string. Returns an element instance representing a comment.
- .. function:: dump(elem)
- Writes an element tree or element structure to sys.stdout. This function should
- be used for debugging only.
- The exact output format is implementation dependent. In this version, it's
- written as an ordinary XML file.
- *elem* is an element tree or an individual element.
- .. function:: Element(tag[, attrib][, **extra])
- Element factory. This function returns an object implementing the standard
- Element interface. The exact class or type of that object is implementation
- dependent, but it will always be compatible with the _ElementInterface class in
- this module.
- The element name, attribute names, and attribute values can be either 8-bit
- ASCII strings or Unicode strings. *tag* is the element name. *attrib* is an
- optional dictionary, containing element attributes. *extra* contains additional
- attributes, given as keyword arguments. Returns an element instance.
- .. function:: fromstring(text)
- Parses an XML section from a string constant. Same as XML. *text* is a string
- containing XML data. Returns an Element instance.
- .. function:: iselement(element)
- Checks if an object appears to be a valid element object. *element* is an
- element instance. Returns a true value if this is an element object.
- .. function:: iterparse(source[, events])
- Parses an XML section into an element tree incrementally, and reports what's
- going on to the user. *source* is a filename or file object containing XML data.
- *events* is a list of events to report back. If omitted, only "end" events are
- reported. Returns an :term:`iterator` providing ``(event, elem)`` pairs.
- .. note::
- :func:`iterparse` only guarantees that it has seen the ">"
- character of a starting tag when it emits a "start" event, so the
- attributes are defined, but the contents of the text and tail attributes
- are undefined at that point. The same applies to the element children;
- they may or may not be present.
- If you need a fully populated element, look for "end" events instead.
- .. function:: parse(source[, parser])
- Parses an XML section into an element tree. *source* is a filename or file
- object containing XML data. *parser* is an optional parser instance. If not
- given, the standard XMLTreeBuilder parser is used. Returns an ElementTree
- instance.
- .. function:: ProcessingInstruction(target[, text])
- PI element factory. This factory function creates a special element that will
- be serialized as an XML processing instruction. *target* is a string containing
- the PI target. *text* is a string containing the PI contents, if given. Returns
- an element instance, representing a processing instruction.
- .. function:: SubElement(parent, tag[, attrib[, **extra]])
- Subelement factory. This function creates an element instance, and appends it
- to an existing element.
- The element name, attribute names, and attribute values can be either 8-bit
- ASCII strings or Unicode strings. *parent* is the parent element. *tag* is the
- subelement name. *attrib* is an optional dictionary, containing element
- attributes. *extra* contains additional attributes, given as keyword arguments.
- Returns an element instance.
- .. function:: tostring(element[, encoding])
- Generates a string representation of an XML element, including all subelements.
- *element* is an Element instance. *encoding* is the output encoding (default is
- US-ASCII). Returns an encoded string containing the XML data.
- .. function:: XML(text)
- Parses an XML section from a string constant. This function can be used to
- embed "XML literals" in Python code. *text* is a string containing XML data.
- Returns an Element instance.
- .. function:: XMLID(text)
- Parses an XML section from a string constant, and also returns a dictionary
- which maps from element id:s to elements. *text* is a string containing XML
- data. Returns a tuple containing an Element instance and a dictionary.
- .. _elementtree-element-interface:
- The Element Interface
- ---------------------
- Element objects returned by Element or SubElement have the following methods
- and attributes.
- .. attribute:: Element.tag
- A string identifying what kind of data this element represents (the element
- type, in other words).
- .. attribute:: Element.text
- The *text* attribute can be used to hold additional data associated with the
- element. As the name implies this attribute is usually a string but may be any
- application-specific object. If the element is created from an XML file the
- attribute will contain any text found between the element tags.
- .. attribute:: Element.tail
- The *tail* attribute can be used to hold additional data associated with the
- element. This attribute is usually a string but may be any application-specific
- object. If the element is created from an XML file the attribute will contain
- any text found after the element's end tag and before the next tag.
- .. attribute:: Element.attrib
- A dictionary containing the element's attributes. Note that while the *attrib*
- value is always a real mutable Python dictionary, an ElementTree implementation
- may choose to use another internal representation, and create the dictionary
- only if someone asks for it. To take advantage of such implementations, use the
- dictionary methods below whenever possible.
- The following dictionary-like methods work on the element attributes.
- .. method:: Element.clear()
- Resets an element. This function removes all subelements, clears all
- attributes, and sets the text and tail attributes to None.
- .. method:: Element.get(key[, default=None])
- Gets the element attribute named *key*.
- Returns the attribute value, or *default* if the attribute was not found.
- .. method:: Element.items()
- Returns the element attributes as a sequence of (name, value) pairs. The
- attributes are returned in an arbitrary order.
- .. method:: Element.keys()
- Returns the elements attribute names as a list. The names are returned in an
- arbitrary order.
- .. method:: Element.set(key, value)
- Set the attribute *key* on the element to *value*.
- The following methods work on the element's children (subelements).
- .. method:: Element.append(subelement)
- Adds the element *subelement* to the end of this elements internal list of
- subelements.
- .. method:: Element.find(match)
- Finds the first subelement matching *match*. *match* may be a tag name or path.
- Returns an element instance or ``None``.
- .. method:: Element.findall(match)
- Finds all subelements matching *match*. *match* may be a tag name or path.
- Returns an iterable yielding all matching elements in document order.
- .. method:: Element.findtext(condition[, default=None])
- Finds text for the first subelement matching *condition*. *condition* may be a
- tag name or path. Returns the text content of the first matching element, or
- *default* if no element was found. Note that if the matching element has no
- text content an empty string is returned.
- .. method:: Element.getchildren()
- Returns all subelements. The elements are returned in document order.
- .. method:: Element.getiterator([tag=None])
- Creates a tree iterator with the current element as the root. The iterator
- iterates over this element and all elements below it that match the given tag.
- If tag is ``None`` or ``'*'`` then all elements are iterated over. Returns an
- iterable that provides element objects in document (depth first) order.
- .. method:: Element.insert(index, element)
- Inserts a subelement at the given position in this element.
- .. method:: Element.makeelement(tag, attrib)
- Creates a new element object of the same type as this element. Do not call this
- method, use the SubElement factory function instead.
- .. method:: Element.remove(subelement)
- Removes *subelement* from the element. Unlike the findXYZ methods this method
- compares elements based on the instance identity, not on tag value or contents.
- Element objects also support the following sequence type methods for working
- with subelements: :meth:`__delitem__`, :meth:`__getitem__`, :meth:`__setitem__`,
- :meth:`__len__`.
- Caution: Because Element objects do not define a :meth:`__nonzero__` method,
- elements with no subelements will test as ``False``. ::
- element = root.find('foo')
- if not element: # careful!
- print "element not found, or element has no subelements"
- if element is None:
- print "element not found"
- .. _elementtree-elementtree-objects:
- ElementTree Objects
- -------------------
- .. class:: ElementTree([element,] [file])
- ElementTree wrapper class. This class represents an entire element hierarchy,
- and adds some extra support for serialization to and from standard XML.
- *element* is the root element. The tree is initialized with the contents of the
- XML *file* if given.
- .. method:: _setroot(element)
- Replaces the root element for this tree. This discards the current
- contents of the tree, and replaces it with the given element. Use with
- care. *element* is an element instance.
- .. method:: find(path)
- Finds the first toplevel element with given tag. Same as
- getroot().find(path). *path* is the element to look for. Returns the
- first matching element, or ``None`` if no element was found.
- .. method:: findall(path)
- Finds all toplevel elements with the given tag. Same as
- getroot().findall(path). *path* is the element to look for. Returns a
- list or :term:`iterator` containing all matching elements, in document
- order.
- .. method:: findtext(path[, default])
- Finds the element text for the first toplevel element with given tag.
- Same as getroot().findtext(path). *path* is the toplevel element to look
- for. *default* is the value to return if the element was not
- found. Returns the text content of the first matching element, or the
- default value no element was found. Note that if the element has is
- found, but has no text content, this method returns an empty string.
- .. method:: getiterator([tag])
- Creates and returns a tree iterator for the root element. The iterator
- loops over all elements in this tree, in section order. *tag* is the tag
- to look for (default is to return all elements)
- .. method:: getroot()
- Returns the root element for this tree.
- .. method:: parse(source[, parser])
- Loads an external XML section into this element tree. *source* is a file
- name or file object. *parser* is an optional parser instance. If not
- given, the standard XMLTreeBuilder parser is used. Returns the section
- root element.
- .. method:: write(file[, encoding])
- Writes the element tree to a file, as XML. *file* is a file name, or a
- file object opened for writing. *encoding* [1]_ is the output encoding
- (default is US-ASCII).
- This is the XML file that is going to be manipulated::
- <html>
- <head>
- <title>Example page</title>
- </head>
- <body>
- <p>Moved to <a href="http://example.org/">example.org</a>
- or <a href="http://example.com/">example.com</a>.</p>
- </body>
- </html>
- Example of changing the attribute "target" of every link in first paragraph::
- >>> from xml.etree.ElementTree import ElementTree
- >>> tree = ElementTree()
- >>> tree.parse("index.xhtml")
- <Element html at b7d3f1ec>
- >>> p = tree.find("body/p") # Finds first occurrence of tag p in body
- >>> p
- <Element p at 8416e0c>
- >>> links = p.getiterator("a") # Returns list of all links
- >>> links
- [<Element a at b7d4f9ec>, <Element a at b7d4fb0c>]
- >>> for i in links: # Iterates through all found links
- ... i.attrib["target"] = "blank"
- >>> tree.write("output.xhtml")
- .. _elementtree-qname-objects:
- QName Objects
- -------------
- .. class:: QName(text_or_uri[, tag])
- QName wrapper. This can be used to wrap a QName attribute value, in order to
- get proper namespace handling on output. *text_or_uri* is a string containing
- the QName value, in the form {uri}local, or, if the tag argument is given, the
- URI part of a QName. If *tag* is given, the first argument is interpreted as an
- URI, and this argument is interpreted as a local name. :class:`QName` instances
- are opaque.
- .. _elementtree-treebuilder-objects:
- TreeBuilder Objects
- -------------------
- .. class:: TreeBuilder([element_factory])
- Generic element structure builder. This builder converts a sequence of start,
- data, and end method calls to a well-formed element structure. You can use this
- class to build an element structure using a custom XML parser, or a parser for
- some other XML-like format. The *element_factory* is called to create new
- Element instances when given.
- .. method:: close()
- Flushes the parser buffers, and returns the toplevel document
- element. Returns an Element instance.
- .. method:: data(data)
- Adds text to the current element. *data* is a string. This should be
- either an 8-bit string containing ASCII text, or a Unicode string.
- .. method:: end(tag)
- Closes the current element. *tag* is the element name. Returns the closed
- element.
- .. method:: start(tag, attrs)
- Opens a new element. *tag* is the element name. *attrs* is a dictionary
- containing element attributes. Returns the opened element.
- .. _elementtree-xmltreebuilder-objects:
- XMLTreeBuilder Objects
- ----------------------
- .. class:: XMLTreeBuilder([html,] [target])
- Element structure builder for XML source data, based on the expat parser. *html*
- are predefined HTML entities. This flag is not supported by the current
- implementation. *target* is the target object. If omitted, the builder uses an
- instance of the standard TreeBuilder class.
- .. method:: close()
- Finishes feeding data to the parser. Returns an element structure.
- .. method:: doctype(name, pubid, system)
- Handles a doctype declaration. *name* is the doctype name. *pubid* is the
- public identifier. *system* is the system identifier.
- .. method:: feed(data)
- Feeds data to the parser. *data* is encoded data.
- :meth:`XMLTreeBuilder.feed` calls *target*\'s :meth:`start` method
- for each opening tag, its :meth:`end` method for each closing tag,
- and data is processed by method :meth:`data`. :meth:`XMLTreeBuilder.close`
- calls *target*\'s method :meth:`close`.
- :class:`XMLTreeBuilder` can be used not only for building a tree structure.
- This is an example of counting the maximum depth of an XML file::
- >>> from xml.etree.ElementTree import XMLTreeBuilder
- >>> class MaxDepth: # The target object of the parser
- ... maxDepth = 0
- ... depth = 0
- ... def start(self, tag, attrib): # Called for each opening tag.
- ... self.depth += 1
- ... if self.depth > self.maxDepth:
- ... self.maxDepth = self.depth
- ... def end(self, tag): # Called for each closing tag.
- ... self.depth -= 1
- ... def data(self, data):
- ... pass # We do not need to do anything with data.
- ... def close(self): # Called when all data has been parsed.
- ... return self.maxDepth
- ...
- >>> target = MaxDepth()
- >>> parser = XMLTreeBuilder(target=target)
- >>> exampleXml = """
- ... <a>
- ... <b>
- ... </b>
- ... <b>
- ... <c>
- ... <d>
- ... </d>
- ... </c>
- ... </b>
- ... </a>"""
- >>> parser.feed(exampleXml)
- >>> parser.close()
- 4
- .. rubric:: Footnotes
- .. [#] The encoding string included in XML output should conform to the
- appropriate standards. For example, "UTF-8" is valid, but "UTF8" is
- not. See http://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
- and http://www.iana.org/assignments/character-sets.