mirror of
https://github.com/python/cpython.git
synced 2024-12-12 03:04:15 +08:00
658 lines
22 KiB
ReStructuredText
658 lines
22 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>
|
|
|
|
**Source code:** :source:`Lib/xml/etree/ElementTree.py`
|
|
|
|
--------------
|
|
|
|
The :class:`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 :class:`Element` constructor or the
|
|
:func:`SubElement` factory function.
|
|
|
|
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.
|
|
|
|
.. versionchanged:: 3.2
|
|
The ElementTree API is updated to 1.3. For more information, see
|
|
`Introducing ElementTree 1.3
|
|
<http://effbot.org/zone/elementtree-13-intro.htm>`_.
|
|
|
|
|
|
.. _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 by the standard serializer. The
|
|
comment string can be either a bytestring 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:: fromstring(text)
|
|
|
|
Parses an XML section from a string constant. Same as :func:`XML`. *text*
|
|
is a string containing XML data. Returns an :class:`Element` instance.
|
|
|
|
|
|
.. function:: fromstringlist(sequence, parser=None)
|
|
|
|
Parses an XML document from a sequence of string fragments. *sequence* is a
|
|
list or other sequence containing XML data fragments. *parser* is an
|
|
optional parser instance. If not given, the standard :class:`XMLParser`
|
|
parser is used. Returns an :class:`Element` instance.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. 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, parser=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. The
|
|
supported events are the strings ``"start"``, ``"end"``, ``"start-ns"``
|
|
and ``"end-ns"`` (the "ns" events are used to get detailed namespace
|
|
information). If *events* is omitted, only ``"end"`` events are reported.
|
|
*parser* is an optional parser instance. If not given, the standard
|
|
:class:`XMLParser` parser is used. *parser* is not supported by
|
|
``cElementTree``. 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 :class:`XMLParser` parser is used. Returns an
|
|
:class:`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:: register_namespace(prefix, uri)
|
|
|
|
Registers a namespace prefix. The registry is global, and any existing
|
|
mapping for either the given prefix or the namespace URI will be removed.
|
|
*prefix* is a namespace prefix. *uri* is a namespace uri. Tags and
|
|
attributes in this namespace will be serialized with the given prefix, if at
|
|
all possible.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. 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
|
|
bytestrings 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="us-ascii", method="xml")
|
|
|
|
Generates a string representation of an XML element, including all
|
|
subelements. *element* is an :class:`Element` instance. *encoding* [1]_ is
|
|
the output encoding (default is US-ASCII). Use ``encoding="unicode"`` to
|
|
generate a Unicode string. *method* is either ``"xml"``,
|
|
``"html"`` or ``"text"`` (default is ``"xml"``). Returns an (optionally)
|
|
encoded string containing the XML data.
|
|
|
|
|
|
.. function:: tostringlist(element, encoding="us-ascii", method="xml")
|
|
|
|
Generates a string representation of an XML element, including all
|
|
subelements. *element* is an :class:`Element` instance. *encoding* [1]_ is
|
|
the output encoding (default is US-ASCII). Use ``encoding="unicode"`` to
|
|
generate a Unicode string. *method* is either ``"xml"``,
|
|
``"html"`` or ``"text"`` (default is ``"xml"``). Returns a list of
|
|
(optionally) encoded strings containing the XML data. It does not guarantee
|
|
any specific sequence, except that ``"".join(tostringlist(element)) ==
|
|
tostring(element)``.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. function:: XML(text, parser=None)
|
|
|
|
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. *parser* is an optional parser instance. If not given, the standard
|
|
:class:`XMLParser` parser is used. Returns an :class:`Element` instance.
|
|
|
|
|
|
.. function:: XMLID(text, parser=None)
|
|
|
|
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. *parser* is an optional parser instance. If not given, the standard
|
|
:class:`XMLParser` parser is used. Returns a tuple containing an
|
|
:class:`Element` instance and a dictionary.
|
|
|
|
|
|
.. _elementtree-element-objects:
|
|
|
|
Element Objects
|
|
---------------
|
|
|
|
|
|
.. class:: Element(tag, attrib={}, **extra)
|
|
|
|
Element class. This class defines the Element interface, and provides a
|
|
reference implementation of this interface.
|
|
|
|
The element name, attribute names, and attribute values can be either
|
|
bytestrings or Unicode strings. *tag* is the element name. *attrib* is
|
|
an optional dictionary, containing element attributes. *extra* contains
|
|
additional attributes, given as keyword arguments.
|
|
|
|
|
|
.. attribute:: tag
|
|
|
|
A string identifying what kind of data this element represents (the
|
|
element type, in other words).
|
|
|
|
|
|
.. attribute:: 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:: 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:: 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:: clear()
|
|
|
|
Resets an element. This function removes all subelements, clears all
|
|
attributes, and sets the text and tail attributes to None.
|
|
|
|
|
|
.. method:: get(key, default=None)
|
|
|
|
Gets the element attribute named *key*.
|
|
|
|
Returns the attribute value, or *default* if the attribute was not found.
|
|
|
|
|
|
.. method:: items()
|
|
|
|
Returns the element attributes as a sequence of (name, value) pairs. The
|
|
attributes are returned in an arbitrary order.
|
|
|
|
|
|
.. method:: keys()
|
|
|
|
Returns the elements attribute names as a list. The names are returned
|
|
in an arbitrary order.
|
|
|
|
|
|
.. method:: set(key, value)
|
|
|
|
Set the attribute *key* on the element to *value*.
|
|
|
|
The following methods work on the element's children (subelements).
|
|
|
|
|
|
.. method:: append(subelement)
|
|
|
|
Adds the element *subelement* to the end of this elements internal list
|
|
of subelements.
|
|
|
|
|
|
.. method:: extend(subelements)
|
|
|
|
Appends *subelements* from a sequence object with zero or more elements.
|
|
Raises :exc:`AssertionError` if a subelement is not a valid object.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. method:: find(match)
|
|
|
|
Finds the first subelement matching *match*. *match* may be a tag name
|
|
or path. Returns an element instance or ``None``.
|
|
|
|
|
|
.. method:: findall(match)
|
|
|
|
Finds all matching subelements, by tag name or path. Returns a list
|
|
containing all matching elements in document order.
|
|
|
|
|
|
.. method:: findtext(match, default=None)
|
|
|
|
Finds text for the first subelement matching *match*. *match* 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:: getchildren()
|
|
|
|
.. deprecated:: 3.2
|
|
Use ``list(elem)`` or iteration.
|
|
|
|
|
|
.. method:: getiterator(tag=None)
|
|
|
|
.. deprecated:: 3.2
|
|
Use method :meth:`Element.iter` instead.
|
|
|
|
|
|
.. method:: insert(index, element)
|
|
|
|
Inserts a subelement at the given position in this element.
|
|
|
|
|
|
.. method:: iter(tag=None)
|
|
|
|
Creates a tree :term:`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. If the
|
|
tree structure is modified during iteration, the result is undefined.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. method:: iterfind(match)
|
|
|
|
Finds all matching subelements, by tag name or path. Returns an iterable
|
|
yielding all matching elements in document order.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. method:: itertext()
|
|
|
|
Creates a text iterator. The iterator loops over this element and all
|
|
subelements, in document order, and returns all inner text.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. method:: makeelement(tag, attrib)
|
|
|
|
Creates a new element object of the same type as this element. Do not
|
|
call this method, use the :func:`SubElement` factory function instead.
|
|
|
|
|
|
.. method:: remove(subelement)
|
|
|
|
Removes *subelement* from the element. Unlike the find\* methods this
|
|
method compares elements based on the instance identity, not on tag value
|
|
or contents.
|
|
|
|
:class:`Element` objects also support the following sequence type methods
|
|
for working with subelements: :meth:`__delitem__`, :meth:`__getitem__`,
|
|
:meth:`__setitem__`, :meth:`__len__`.
|
|
|
|
Caution: Elements with no subelements will test as ``False``. This behavior
|
|
will change in future versions. Use specific ``len(elem)`` or ``elem is
|
|
None`` test instead. ::
|
|
|
|
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(match)
|
|
|
|
Finds the first toplevel element matching *match*. *match* may be a tag
|
|
name or path. Same as getroot().find(match). Returns the first matching
|
|
element, or ``None`` if no element was found.
|
|
|
|
|
|
.. method:: findall(match)
|
|
|
|
Finds all matching subelements, by tag name or path. Same as
|
|
getroot().findall(match). *match* may be a tag name or path. Returns a
|
|
list containing all matching elements, in document order.
|
|
|
|
|
|
.. method:: findtext(match, default=None)
|
|
|
|
Finds the element text for the first toplevel element with given tag.
|
|
Same as getroot().findtext(match). *match* may be a tag name or path.
|
|
*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 is found, but has no text
|
|
content, this method returns an empty string.
|
|
|
|
|
|
.. method:: getiterator(tag=None)
|
|
|
|
.. deprecated:: 3.2
|
|
Use method :meth:`ElementTree.iter` instead.
|
|
|
|
|
|
.. method:: getroot()
|
|
|
|
Returns the root element for this tree.
|
|
|
|
|
|
.. method:: iter(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:: iterfind(match)
|
|
|
|
Finds all matching subelements, by tag name or path. Same as
|
|
getroot().iterfind(match). Returns an iterable yielding all matching
|
|
elements in document order.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. 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 XMLParser parser is used. Returns the section
|
|
root element.
|
|
|
|
|
|
.. method:: write(file, encoding="us-ascii", xml_declaration=None, \
|
|
default_namespace=None, method="xml")
|
|
|
|
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). Use ``encoding="unicode"`` to write a
|
|
Unicode string. *xml_declaration* controls if an XML declaration
|
|
should be added to the file. Use False for never, True for always, None
|
|
for only if not US-ASCII or UTF-8 or Unicode (default is None).
|
|
*default_namespace* sets the default XML namespace (for "xmlns").
|
|
*method* is either ``"xml"``, ``"html"`` or ``"text"`` (default is
|
|
``"xml"``). Returns an (optionally) encoded string.
|
|
|
|
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 0xb77e6fac>
|
|
>>> p = tree.find("body/p") # Finds first occurrence of tag p in body
|
|
>>> p
|
|
<Element 'p' at 0xb77ec26c>
|
|
>>> links = list(p.iter("a")) # Returns list of all links
|
|
>>> links
|
|
[<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
|
|
>>> 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 :class:`Element` instances when given.
|
|
|
|
|
|
.. method:: close()
|
|
|
|
Flushes the builder buffers, and returns the toplevel document
|
|
element. Returns an :class:`Element` instance.
|
|
|
|
|
|
.. method:: data(data)
|
|
|
|
Adds text to the current element. *data* is a string. This should be
|
|
either a bytestring, 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.
|
|
|
|
|
|
In addition, a custom :class:`TreeBuilder` object can provide the
|
|
following method:
|
|
|
|
.. method:: doctype(name, pubid, system)
|
|
|
|
Handles a doctype declaration. *name* is the doctype name. *pubid* is
|
|
the public identifier. *system* is the system identifier. This method
|
|
does not exist on the default :class:`TreeBuilder` class.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. _elementtree-xmlparser-objects:
|
|
|
|
XMLParser Objects
|
|
-----------------
|
|
|
|
|
|
.. class:: XMLParser(html=0, target=None, encoding=None)
|
|
|
|
:class:`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. *encoding* [1]_
|
|
is optional. If given, the value overrides the encoding specified in the
|
|
XML file.
|
|
|
|
|
|
.. method:: close()
|
|
|
|
Finishes feeding data to the parser. Returns an element structure.
|
|
|
|
|
|
.. method:: doctype(name, pubid, system)
|
|
|
|
.. deprecated:: 3.2
|
|
Define the :meth:`TreeBuilder.doctype` method on a custom TreeBuilder
|
|
target.
|
|
|
|
|
|
.. method:: feed(data)
|
|
|
|
Feeds data to the parser. *data* is encoded data.
|
|
|
|
:meth:`XMLParser.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:`XMLParser.close`
|
|
calls *target*\'s method :meth:`close`.
|
|
:class:`XMLParser` 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 XMLParser
|
|
>>> 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 = XMLParser(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.
|