
``xml.etree.ElementTree`` --- The ElementTree XML API
*****************************************************

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 ``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
``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.


Functions
=========

xml.etree.ElementTree.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 ASCII-only ``bytes`` object or a ``str``
   object. *text* is a string containing the comment string. Returns
   an element instance representing a comment.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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 ``bytes`` object or a ``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.

xml.etree.ElementTree.fromstring(text)

   Parses an XML section from a string constant.  Same as XML. *text*
   is a string containing XML data. Returns an Element instance.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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.

   Note: ``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.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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 ``bytes`` object or a ``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.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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.


The Element Interface
=====================

Element objects returned by Element or SubElement have the  following
methods and attributes.

Element.tag

   A string identifying what kind of data this element represents (the
   element type, in other words).

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.

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.

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.

Element.clear()

   Resets an element.  This function removes all subelements, clears
   all attributes, and sets the text and tail attributes to None.

Element.get(key[, default=None])

   Gets the element attribute named *key*.

   Returns the attribute value, or *default* if the attribute was not
   found.

Element.items()

   Returns the element attributes as a sequence of (name, value)
   pairs. The attributes are returned in an arbitrary order.

Element.keys()

   Returns the elements attribute names as a list. The names are
   returned in an arbitrary order.

Element.set(key, value)

   Set the attribute *key* on the element to *value*.

The following methods work on the element's children (subelements).

Element.append(subelement)

   Adds the element *subelement* to the end of this elements internal
   list of subelements.

Element.find(match)

   Finds the first subelement matching *match*.  *match* may be a tag
   name or path. Returns an element instance or ``None``.

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.

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.

Element.getchildren()

   Returns all subelements.  The elements are returned in document
   order.

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.

Element.insert(index, element)

   Inserts a subelement at the given position in this element.

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.

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: ``__delitem__()``, ``__getitem__()``,
``__setitem__()``, ``__len__()``.

Caution: Because Element objects do not define a ``__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 Objects
===================

class xml.etree.ElementTree.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.

   _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.

   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.

   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.

   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.

   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)

   getroot()

      Returns the root element for this tree.

   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.

   write(file[, encoding])

      Writes the element tree to a file, as XML. *file* is a file
      name, or a file object opened for writing. *encoding* [1] is the
      output encoding (default is US-ASCII).

This is the XML file that is going to be manipulated:

   <html>
       <head>
           <title>Example page</title>
       </head>
       <body>
           <p>Moved to <a href="http://example.org/">example.org</a>
           or <a href="http://example.com/">example.com</a>.</p>
       </body>
   </html>

Example of changing the attribute "target" of every link in first
paragraph:

   >>> from xml.etree.ElementTree import ElementTree
   >>> tree = ElementTree()
   >>> tree.parse("index.xhtml")
   <Element html at b7d3f1ec>
   >>> p = tree.find("body/p")     # Finds first occurrence of tag p in body
   >>> p
   <Element p at 8416e0c>
   >>> links = p.getiterator("a")  # Returns list of all links
   >>> links
   [<Element a at b7d4f9ec>, <Element a at b7d4fb0c>]
   >>> for i in links:             # Iterates through all found links
   ...     i.attrib["target"] = "blank"
   >>> tree.write("output.xhtml")


QName Objects
=============

class xml.etree.ElementTree.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. ``QName`` instances are
   opaque.


TreeBuilder Objects
===================

class xml.etree.ElementTree.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.

   close()

      Flushes the parser buffers, and returns the toplevel document
      element. Returns an Element instance.

   data(data)

      Adds text to the current element. *data* is a string.  This
      should be either an ASCII-only ``bytes`` object or a ``str``
      object.

   end(tag)

      Closes the current element. *tag* is the element name. Returns
      the closed element.

   start(tag, attrs)

      Opens a new element. *tag* is the element name. *attrs* is a
      dictionary containing element attributes. Returns the opened
      element.


XMLTreeBuilder Objects
======================

class xml.etree.ElementTree.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.

   close()

      Finishes feeding data to the parser. Returns an element
      structure.

   doctype(name, pubid, system)

      Handles a doctype declaration. *name* is the doctype name.
      *pubid* is the public identifier. *system* is the system
      identifier.

   feed(data)

      Feeds data to the parser. *data* is encoded data.

``XMLTreeBuilder.feed()`` calls *target*'s ``start()`` method for each
opening tag, its ``end()`` method for each closing tag, and data is
processed by method ``data()``. ``XMLTreeBuilder.close()`` calls
*target*'s method ``close()``. ``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

-[ Footnotes ]-

[1] 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 .
