mirror of https://github.com/python/cpython
534 lines
17 KiB
ReStructuredText
534 lines
17 KiB
ReStructuredText
:mod:`xml.etree.ElementTree` --- The ElementTree XML API
|
|
========================================================
|
|
|
|
.. module:: xml.etree.ElementTree
|
|
:synopsis: Implementation of the ElementTree API.
|
|
.. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>
|
|
|
|
|
|
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=None)
|
|
|
|
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 ASCII-only :class:`bytes` object or a :class:`str` object. *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 an
|
|
ASCII-only :class:`bytes` object or a :class:`str` object. *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=None)
|
|
|
|
Parses an XML section into an element tree incrementally, and reports what's
|
|
going on to the user. *source* is a filename or :term:`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=None)
|
|
|
|
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=None)
|
|
|
|
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 an ASCII-only
|
|
:class:`bytes` object or a :class:`str` object. *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=None)
|
|
|
|
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, in document (depth first)
|
|
order. If *tag* is not ``None`` or ``'*'``, only elements whose tag equals
|
|
*tag* are returned from the iterator.
|
|
|
|
|
|
.. 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:`__bool__` 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=None, file=None)
|
|
|
|
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=None)
|
|
|
|
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=None)
|
|
|
|
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=None)
|
|
|
|
Loads an external XML section into this element tree. *source* is a file
|
|
name or :term:`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=None)
|
|
|
|
Writes the element tree to a file, as XML. *file* is a file name, or a
|
|
:term:`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=None)
|
|
|
|
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=None)
|
|
|
|
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 ASCII-only :class:`bytes` object or a :class:`str` object.
|
|
|
|
|
|
.. 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=0, target=None)
|
|
|
|
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.
|
|
|