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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`.
+
+
+.. _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 iterator providing ``(event, elem)`` pairs.
+
+
+.. 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:: ElementTree._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:: ElementTree.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:: ElementTree.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 iterator containing all
+   matching elements, in document order.
+
+
+.. method:: ElementTree.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:: ElementTree.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:: ElementTree.getroot()
+
+   Returns the root element for this tree.
+
+
+.. method:: ElementTree.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:: ElementTree.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* is the output encoding (default is
+   US-ASCII).
+
+
+.. _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:: TreeBuilder.close()
+
+   Flushes the parser buffers, and returns the toplevel documen element. Returns an
+   Element instance.
+
+
+.. method:: TreeBuilder.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:: TreeBuilder.end(tag)
+
+   Closes the current element. *tag* is the element name. Returns the closed
+   element.
+
+
+.. method:: TreeBuilder.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:: XMLTreeBuilder.close()
+
+   Finishes feeding data to the parser. Returns an element structure.
+
+
+.. method:: XMLTreeBuilder.doctype(name, pubid, system)
+
+   Handles a doctype declaration. *name* is the doctype name. *pubid* is the public
+   identifier. *system* is the system identifier.
+
+
+.. method:: XMLTreeBuilder.feed(data)
+
+   Feeds data to the parser. *data* is encoded data.
+