652 lines
21 KiB
ReStructuredText
652 lines
21 KiB
ReStructuredText
:mod:`xml.etree.ElementTree` --- The ElementTree XML API
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========================================================
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.. module:: xml.etree.ElementTree
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:synopsis: Implementation of the ElementTree API.
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.. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>
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.. versionadded:: 2.5
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**Source code:** :source:`Lib/xml/etree/ElementTree.py`
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--------------
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The :class:`Element` type is a flexible container object, designed to store
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hierarchical data structures in memory. The type can be described as a cross
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between a list and a dictionary.
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Each element has a number of properties associated with it:
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* a tag which is a string identifying what kind of data this element represents
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(the element type, in other words).
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* a number of attributes, stored in a Python dictionary.
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* a text string.
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* an optional tail string.
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* a number of child elements, stored in a Python sequence
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To create an element instance, use the :class:`Element` constructor or the
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:func:`SubElement` factory function.
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The :class:`ElementTree` class can be used to wrap an element structure, and
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convert it from and to XML.
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A C implementation of this API is available as :mod:`xml.etree.cElementTree`.
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See http://effbot.org/zone/element-index.htm for tutorials and links to other
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docs. Fredrik Lundh's page is also the location of the development version of
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the xml.etree.ElementTree.
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.. versionchanged:: 2.7
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The ElementTree API is updated to 1.3. For more information, see
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`Introducing ElementTree 1.3
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<http://effbot.org/zone/elementtree-13-intro.htm>`_.
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.. _elementtree-functions:
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Functions
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---------
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.. function:: Comment(text=None)
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Comment element factory. This factory function creates a special element
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that will be serialized as an XML comment by the standard serializer. The
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comment string can be either a bytestring or a Unicode string. *text* is a
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string containing the comment string. Returns an element instance
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representing a comment.
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.. function:: dump(elem)
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Writes an element tree or element structure to sys.stdout. This function
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should be used for debugging only.
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The exact output format is implementation dependent. In this version, it's
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written as an ordinary XML file.
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*elem* is an element tree or an individual element.
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.. function:: fromstring(text)
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Parses an XML section from a string constant. Same as :func:`XML`. *text*
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is a string containing XML data. Returns an :class:`Element` instance.
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.. function:: fromstringlist(sequence, parser=None)
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Parses an XML document from a sequence of string fragments. *sequence* is a
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list or other sequence containing XML data fragments. *parser* is an
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optional parser instance. If not given, the standard :class:`XMLParser`
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parser is used. Returns an :class:`Element` instance.
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.. versionadded:: 2.7
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.. function:: iselement(element)
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Checks if an object appears to be a valid element object. *element* is an
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element instance. Returns a true value if this is an element object.
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.. function:: iterparse(source, events=None, parser=None)
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Parses an XML section into an element tree incrementally, and reports what's
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going on to the user. *source* is a filename or file object containing XML
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data. *events* is a list of events to report back. If omitted, only "end"
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events are reported. *parser* is an optional parser instance. If not
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given, the standard :class:`XMLParser` parser is used. Returns an
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:term:`iterator` providing ``(event, elem)`` pairs.
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.. note::
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:func:`iterparse` only guarantees that it has seen the ">"
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character of a starting tag when it emits a "start" event, so the
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attributes are defined, but the contents of the text and tail attributes
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are undefined at that point. The same applies to the element children;
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they may or may not be present.
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If you need a fully populated element, look for "end" events instead.
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.. function:: parse(source, parser=None)
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Parses an XML section into an element tree. *source* is a filename or file
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object containing XML data. *parser* is an optional parser instance. If
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not given, the standard :class:`XMLParser` parser is used. Returns an
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:class:`ElementTree` instance.
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.. function:: ProcessingInstruction(target, text=None)
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PI element factory. This factory function creates a special element that
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will be serialized as an XML processing instruction. *target* is a string
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containing the PI target. *text* is a string containing the PI contents, if
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given. Returns an element instance, representing a processing instruction.
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.. function:: register_namespace(prefix, uri)
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Registers a namespace prefix. The registry is global, and any existing
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mapping for either the given prefix or the namespace URI will be removed.
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*prefix* is a namespace prefix. *uri* is a namespace uri. Tags and
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attributes in this namespace will be serialized with the given prefix, if at
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all possible.
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.. versionadded:: 2.7
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.. function:: SubElement(parent, tag, attrib={}, **extra)
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Subelement factory. This function creates an element instance, and appends
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it to an existing element.
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The element name, attribute names, and attribute values can be either
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bytestrings or Unicode strings. *parent* is the parent element. *tag* is
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the subelement name. *attrib* is an optional dictionary, containing element
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attributes. *extra* contains additional attributes, given as keyword
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arguments. Returns an element instance.
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.. function:: tostring(element, encoding="us-ascii", method="xml")
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Generates a string representation of an XML element, including all
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subelements. *element* is an :class:`Element` instance. *encoding* [1]_ is
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the output encoding (default is US-ASCII). *method* is either ``"xml"``,
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``"html"`` or ``"text"`` (default is ``"xml"``). Returns an encoded string
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containing the XML data.
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.. function:: tostringlist(element, encoding="us-ascii", method="xml")
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Generates a string representation of an XML element, including all
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subelements. *element* is an :class:`Element` instance. *encoding* [1]_ is
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the output encoding (default is US-ASCII). *method* is either ``"xml"``,
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``"html"`` or ``"text"`` (default is ``"xml"``). Returns a list of encoded
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strings containing the XML data. It does not guarantee any specific
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sequence, except that ``"".join(tostringlist(element)) ==
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tostring(element)``.
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.. versionadded:: 2.7
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.. function:: XML(text, parser=None)
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Parses an XML section from a string constant. This function can be used to
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embed "XML literals" in Python code. *text* is a string containing XML
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data. *parser* is an optional parser instance. If not given, the standard
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:class:`XMLParser` parser is used. Returns an :class:`Element` instance.
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.. function:: XMLID(text, parser=None)
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Parses an XML section from a string constant, and also returns a dictionary
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which maps from element id:s to elements. *text* is a string containing XML
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data. *parser* is an optional parser instance. If not given, the standard
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:class:`XMLParser` parser is used. Returns a tuple containing an
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:class:`Element` instance and a dictionary.
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.. _elementtree-element-objects:
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Element Objects
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---------------
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.. class:: Element(tag, attrib={}, **extra)
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Element class. This class defines the Element interface, and provides a
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reference implementation of this interface.
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The element name, attribute names, and attribute values can be either
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bytestrings or Unicode strings. *tag* is the element name. *attrib* is
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an optional dictionary, containing element attributes. *extra* contains
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additional attributes, given as keyword arguments.
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.. attribute:: tag
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A string identifying what kind of data this element represents (the
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element type, in other words).
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.. attribute:: text
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The *text* attribute can be used to hold additional data associated with
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the element. As the name implies this attribute is usually a string but
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may be any application-specific object. If the element is created from
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an XML file the attribute will contain any text found between the element
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tags.
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.. attribute:: tail
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The *tail* attribute can be used to hold additional data associated with
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the element. This attribute is usually a string but may be any
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application-specific object. If the element is created from an XML file
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the attribute will contain any text found after the element's end tag and
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before the next tag.
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.. attribute:: attrib
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A dictionary containing the element's attributes. Note that while the
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*attrib* value is always a real mutable Python dictionary, an ElementTree
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implementation may choose to use another internal representation, and
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create the dictionary only if someone asks for it. To take advantage of
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such implementations, use the dictionary methods below whenever possible.
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The following dictionary-like methods work on the element attributes.
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.. method:: clear()
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Resets an element. This function removes all subelements, clears all
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attributes, and sets the text and tail attributes to None.
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.. method:: get(key, default=None)
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Gets the element attribute named *key*.
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Returns the attribute value, or *default* if the attribute was not found.
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.. method:: items()
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Returns the element attributes as a sequence of (name, value) pairs. The
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attributes are returned in an arbitrary order.
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.. method:: keys()
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Returns the elements attribute names as a list. The names are returned
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in an arbitrary order.
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.. method:: set(key, value)
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Set the attribute *key* on the element to *value*.
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The following methods work on the element's children (subelements).
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.. method:: append(subelement)
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Adds the element *subelement* to the end of this elements internal list
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of subelements.
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.. method:: extend(subelements)
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Appends *subelements* from a sequence object with zero or more elements.
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Raises :exc:`AssertionError` if a subelement is not a valid object.
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.. versionadded:: 2.7
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.. method:: find(match)
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Finds the first subelement matching *match*. *match* may be a tag name
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or path. Returns an element instance or ``None``.
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.. method:: findall(match)
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Finds all matching subelements, by tag name or path. Returns a list
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containing all matching elements in document order.
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.. method:: findtext(match, default=None)
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Finds text for the first subelement matching *match*. *match* may be
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a tag name or path. Returns the text content of the first matching
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element, or *default* if no element was found. Note that if the matching
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element has no text content an empty string is returned.
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.. method:: getchildren()
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.. deprecated:: 2.7
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Use ``list(elem)`` or iteration.
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.. method:: getiterator(tag=None)
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.. deprecated:: 2.7
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Use method :meth:`Element.iter` instead.
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.. method:: insert(index, element)
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Inserts a subelement at the given position in this element.
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.. method:: iter(tag=None)
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Creates a tree :term:`iterator` with the current element as the root.
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The iterator iterates over this element and all elements below it, in
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document (depth first) order. If *tag* is not ``None`` or ``'*'``, only
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elements whose tag equals *tag* are returned from the iterator. If the
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tree structure is modified during iteration, the result is undefined.
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.. versionadded:: 2.7
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.. method:: iterfind(match)
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Finds all matching subelements, by tag name or path. Returns an iterable
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yielding all matching elements in document order.
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.. versionadded:: 2.7
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.. method:: itertext()
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Creates a text iterator. The iterator loops over this element and all
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subelements, in document order, and returns all inner text.
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.. versionadded:: 2.7
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.. method:: makeelement(tag, attrib)
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Creates a new element object of the same type as this element. Do not
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call this method, use the :func:`SubElement` factory function instead.
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.. method:: remove(subelement)
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Removes *subelement* from the element. Unlike the find\* methods this
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method compares elements based on the instance identity, not on tag value
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or contents.
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:class:`Element` objects also support the following sequence type methods
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for working with subelements: :meth:`__delitem__`, :meth:`__getitem__`,
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:meth:`__setitem__`, :meth:`__len__`.
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Caution: Elements with no subelements will test as ``False``. This behavior
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will change in future versions. Use specific ``len(elem)`` or ``elem is
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None`` test instead. ::
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element = root.find('foo')
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if not element: # careful!
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print "element not found, or element has no subelements"
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if element is None:
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print "element not found"
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.. _elementtree-elementtree-objects:
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ElementTree Objects
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-------------------
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.. class:: ElementTree(element=None, file=None)
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ElementTree wrapper class. This class represents an entire element
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hierarchy, and adds some extra support for serialization to and from
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standard XML.
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*element* is the root element. The tree is initialized with the contents
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of the XML *file* if given.
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.. method:: _setroot(element)
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Replaces the root element for this tree. This discards the current
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contents of the tree, and replaces it with the given element. Use with
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care. *element* is an element instance.
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.. method:: find(match)
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Finds the first toplevel element matching *match*. *match* may be a tag
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name or path. Same as getroot().find(match). Returns the first matching
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element, or ``None`` if no element was found.
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.. method:: findall(match)
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Finds all matching subelements, by tag name or path. Same as
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getroot().findall(match). *match* may be a tag name or path. Returns a
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list containing all matching elements, in document order.
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.. method:: findtext(match, default=None)
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Finds the element text for the first toplevel element with given tag.
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Same as getroot().findtext(match). *match* may be a tag name or path.
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*default* is the value to return if the element was not found. Returns
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the text content of the first matching element, or the default value no
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element was found. Note that if the element is found, but has no text
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content, this method returns an empty string.
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.. method:: getiterator(tag=None)
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.. deprecated:: 2.7
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Use method :meth:`ElementTree.iter` instead.
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.. method:: getroot()
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Returns the root element for this tree.
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.. method:: iter(tag=None)
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Creates and returns a tree iterator for the root element. The iterator
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loops over all elements in this tree, in section order. *tag* is the tag
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to look for (default is to return all elements)
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.. method:: iterfind(match)
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Finds all matching subelements, by tag name or path. Same as
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getroot().iterfind(match). Returns an iterable yielding all matching
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elements in document order.
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.. versionadded:: 2.7
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.. method:: parse(source, parser=None)
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Loads an external XML section into this element tree. *source* is a file
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name or file object. *parser* is an optional parser instance. If not
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given, the standard XMLParser parser is used. Returns the section
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root element.
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.. method:: write(file, encoding="us-ascii", xml_declaration=None, method="xml")
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Writes the element tree to a file, as XML. *file* is a file name, or a
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file object opened for writing. *encoding* [1]_ is the output encoding
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(default is US-ASCII). *xml_declaration* controls if an XML declaration
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should be added to the file. Use False for never, True for always, None
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for only if not US-ASCII or UTF-8 (default is None). *method* is either
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``"xml"``, ``"html"`` or ``"text"`` (default is ``"xml"``). Returns an
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encoded string.
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This is the XML file that is going to be manipulated::
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<html>
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<head>
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<title>Example page</title>
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</head>
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<body>
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<p>Moved to <a href="http://example.org/">example.org</a>
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or <a href="http://example.com/">example.com</a>.</p>
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</body>
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</html>
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Example of changing the attribute "target" of every link in first paragraph::
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>>> from xml.etree.ElementTree import ElementTree
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>>> tree = ElementTree()
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>>> tree.parse("index.xhtml")
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<Element 'html' at 0xb77e6fac>
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>>> p = tree.find("body/p") # Finds first occurrence of tag p in body
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>>> p
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<Element 'p' at 0xb77ec26c>
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>>> links = list(p.iter("a")) # Returns list of all links
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>>> links
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[<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
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>>> for i in links: # Iterates through all found links
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... i.attrib["target"] = "blank"
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>>> tree.write("output.xhtml")
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.. _elementtree-qname-objects:
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QName Objects
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-------------
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.. class:: QName(text_or_uri, tag=None)
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QName wrapper. This can be used to wrap a QName attribute value, in order
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to get proper namespace handling on output. *text_or_uri* is a string
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containing the QName value, in the form {uri}local, or, if the tag argument
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is given, the URI part of a QName. If *tag* is given, the first argument is
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interpreted as an URI, and this argument is interpreted as a local name.
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:class:`QName` instances are opaque.
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.. _elementtree-treebuilder-objects:
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TreeBuilder Objects
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-------------------
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.. class:: TreeBuilder(element_factory=None)
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Generic element structure builder. This builder converts a sequence of
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start, data, and end method calls to a well-formed element structure. You
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can use this class to build an element structure using a custom XML parser,
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or a parser for some other XML-like format. The *element_factory* is called
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to create new :class:`Element` instances when given.
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.. method:: close()
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Flushes the builder buffers, and returns the toplevel document
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element. Returns an :class:`Element` instance.
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.. method:: data(data)
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Adds text to the current element. *data* is a string. This should be
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either a bytestring, or a Unicode string.
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.. method:: end(tag)
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Closes the current element. *tag* is the element name. Returns the
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closed element.
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.. method:: start(tag, attrs)
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Opens a new element. *tag* is the element name. *attrs* is a dictionary
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containing element attributes. Returns the opened element.
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In addition, a custom :class:`TreeBuilder` object can provide the
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following method:
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.. method:: doctype(name, pubid, system)
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Handles a doctype declaration. *name* is the doctype name. *pubid* is
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the public identifier. *system* is the system identifier. This method
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|
does not exist on the default :class:`TreeBuilder` class.
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.. versionadded:: 2.7
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.. _elementtree-xmlparser-objects:
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XMLParser Objects
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-----------------
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.. class:: XMLParser(html=0, target=None, encoding=None)
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:class:`Element` structure builder for XML source data, based on the expat
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|
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.
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|
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|
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.. method:: close()
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|
|
Finishes feeding data to the parser. Returns an element structure.
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|
|
.. method:: doctype(name, pubid, system)
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|
|
.. deprecated:: 2.7
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|
Define the :meth:`TreeBuilder.doctype` method on a custom TreeBuilder
|
|
target.
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|
|
.. method:: feed(data)
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|
|
|
Feeds data to the parser. *data* is encoded data.
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|
|
|
: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::
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|
|
|
>>> 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
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|
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|
.. rubric:: Footnotes
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|
|
|
.. [#] 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.
|