cpython/Doc/library/xml.etree.elementtree.rst

:mod:`xml.etree.ElementTree` --- The ElementTree XML API
========================================================

.. module:: xml.etree.ElementTree
   :synopsis: Implementation of the ElementTree API.
.. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>

The :mod:`xml.etree.ElementTree` module implements a simple and efficient API
for parsing and creating XML data.

.. versionchanged:: 3.3
   This module will use a fast implementation whenever available.
   The :mod:`xml.etree.cElementTree` module is deprecated.


.. warning::

   The :mod:`xml.etree.ElementTree` module is not secure against
   maliciously constructed data.  If you need to parse untrusted or
   unauthenticated data see :ref:`xml-vulnerabilities`.

Tutorial
--------

This is a short tutorial for using :mod:`xml.etree.ElementTree` (``ET`` in
short).  The goal is to demonstrate some of the building blocks and basic
concepts of the module.

XML tree and elements
^^^^^^^^^^^^^^^^^^^^^

XML is an inherently hierarchical data format, and the most natural way to
represent it is with a tree.  ``ET`` has two classes for this purpose -
:class:`ElementTree` represents the whole XML document as a tree, and
:class:`Element` represents a single node in this tree.  Interactions with
the whole document (reading and writing to/from files) are usually done
on the :class:`ElementTree` level.  Interactions with a single XML element
and its sub-elements are done on the :class:`Element` level.

.. _elementtree-parsing-xml:

Parsing XML
^^^^^^^^^^^

We'll be using the following XML document as the sample data for this section:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank>1</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank>4</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank>68</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

We can import this data by reading from a file::

   import xml.etree.ElementTree as ET
   tree = ET.parse('country_data.xml')
   root = tree.getroot()

Or directly from a string::

   root = ET.fromstring(country_data_as_string)

:func:`fromstring` parses XML from a string directly into an :class:`Element`,
which is the root element of the parsed tree.  Other parsing functions may
create an :class:`ElementTree`.  Check the documentation to be sure.

As an :class:`Element`, ``root`` has a tag and a dictionary of attributes::

   >>> root.tag
   'data'
   >>> root.attrib
   {}

It also has children nodes over which we can iterate::

   >>> for child in root:
   ...   print(child.tag, child.attrib)
   ...
   country {'name': 'Liechtenstein'}
   country {'name': 'Singapore'}
   country {'name': 'Panama'}

Children are nested, and we can access specific child nodes by index::

   >>> root[0][1].text
   '2008'

Incremental parsing
^^^^^^^^^^^^^^^^^^^

It's possible to parse XML incrementally (i.e. not the whole document at once).
The most powerful tool for doing this is :class:`IncrementalParser`.  It does
not require a blocking read to obtain the XML data, and is instead fed with
data incrementally with :meth:`IncrementalParser.data_received` calls.  To get
the parsed XML elements, call :meth:`IncrementalParser.events`.  Here's an
example::

    >>> incparser = ET.IncrementalParser(['start', 'end'])
    >>> incparser.data_received('<mytag>sometext')
    >>> list(incparser.events())
    [('start', <Element 'mytag' at 0x7fba3f2a8688>)]
    >>> incparser.data_received(' more text</mytag>')
    >>> for event, elem in incparser.events():
    ...   print(event)
    ...   print(elem.tag, 'text=', elem.text)
    ...
    end
    mytag text= sometext more text

The obvious use case is applications that operate in an asynchronous fashion
where the XML data is being received from a socket or read incrementally from
some storage device.  In such cases, blocking reads are unacceptable.

Because it's so flexible, :class:`IncrementalParser` can be inconvenient
to use for simpler use-cases.  If you don't mind your application blocking on
reading XML data but would still like to have incremental parsing capabilities,
take a look at :func:`iterparse`.  It can be useful when you're reading a large
XML document and don't want to hold it wholly in memory.

Finding interesting elements
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:class:`Element` has some useful methods that help iterate recursively over all
the sub-tree below it (its children, their children, and so on).  For example,
:meth:`Element.iter`::

   >>> for neighbor in root.iter('neighbor'):
   ...   print(neighbor.attrib)
   ...
   {'name': 'Austria', 'direction': 'E'}
   {'name': 'Switzerland', 'direction': 'W'}
   {'name': 'Malaysia', 'direction': 'N'}
   {'name': 'Costa Rica', 'direction': 'W'}
   {'name': 'Colombia', 'direction': 'E'}

:meth:`Element.findall` finds only elements with a tag which are direct
children of the current element.  :meth:`Element.find` finds the *first* child
with a particular tag, and :meth:`Element.text` accesses the element's text
content.  :meth:`Element.get` accesses the element's attributes::

   >>> for country in root.findall('country'):
   ...   rank = country.find('rank').text
   ...   name = country.get('name')
   ...   print(name, rank)
   ...
   Liechtenstein 1
   Singapore 4
   Panama 68

More sophisticated specification of which elements to look for is possible by
using :ref:`XPath <elementtree-xpath>`.

Modifying an XML File
^^^^^^^^^^^^^^^^^^^^^

:class:`ElementTree` provides a simple way to build XML documents and write them to files.
The :meth:`ElementTree.write` method serves this purpose.

Once created, an :class:`Element` object may be manipulated by directly changing
its fields (such as :attr:`Element.text`), adding and modifying attributes
(:meth:`Element.set` method), as well as adding new children (for example
with :meth:`Element.append`).

Let's say we want to add one to each country's rank, and add an ``updated``
attribute to the rank element::

   >>> for rank in root.iter('rank'):
   ...   new_rank = int(rank.text) + 1
   ...   rank.text = str(new_rank)
   ...   rank.set('updated', 'yes')
   ...
   >>> tree.write('output.xml')

Our XML now looks like this:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank updated="yes">69</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

We can remove elements using :meth:`Element.remove`.  Let's say we want to
remove all countries with a rank higher than 50::

   >>> for country in root.findall('country'):
   ...   rank = int(country.find('rank').text)
   ...   if rank > 50:
   ...     root.remove(country)
   ...
   >>> tree.write('output.xml')

Our XML now looks like this:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
   </data>

Building XML documents
^^^^^^^^^^^^^^^^^^^^^^

The :func:`SubElement` function also provides a convenient way to create new
sub-elements for a given element::

   >>> a = ET.Element('a')
   >>> b = ET.SubElement(a, 'b')
   >>> c = ET.SubElement(a, 'c')
   >>> d = ET.SubElement(c, 'd')
   >>> ET.dump(a)
   <a><b /><c><d /></c></a>

Additional resources
^^^^^^^^^^^^^^^^^^^^

See http://effbot.org/zone/element-index.htm for tutorials and links to other
docs.


.. _elementtree-xpath:

XPath support
-------------

This module provides limited support for
`XPath expressions <http://www.w3.org/TR/xpath>`_ for locating elements in a
tree.  The goal is to support a small subset of the abbreviated syntax; a full
XPath engine is outside the scope of the module.

Example
^^^^^^^

Here's an example that demonstrates some of the XPath capabilities of the
module.  We'll be using the ``countrydata`` XML document from the
:ref:`Parsing XML <elementtree-parsing-xml>` section::

   import xml.etree.ElementTree as ET

   root = ET.fromstring(countrydata)

   # Top-level elements
   root.findall(".")

   # All 'neighbor' grand-children of 'country' children of the top-level
   # elements
   root.findall("./country/neighbor")

   # Nodes with name='Singapore' that have a 'year' child
   root.findall(".//year/..[@name='Singapore']")

   # 'year' nodes that are children of nodes with name='Singapore'
   root.findall(".//*[@name='Singapore']/year")

   # All 'neighbor' nodes that are the second child of their parent
   root.findall(".//neighbor[2]")

Supported XPath syntax
^^^^^^^^^^^^^^^^^^^^^^

.. tabularcolumns:: |l|L|

+-----------------------+------------------------------------------------------+
| Syntax                | Meaning                                              |
+=======================+======================================================+
| ``tag``               | Selects all child elements with the given tag.       |
|                       | For example, ``spam`` selects all child elements     |
|                       | named ``spam``, ``spam/egg`` selects all             |
|                       | grandchildren named ``egg`` in all children named    |
|                       | ``spam``.                                            |
+-----------------------+------------------------------------------------------+
| ``*``                 | Selects all child elements.  For example, ``*/egg``  |
|                       | selects all grandchildren named ``egg``.             |
+-----------------------+------------------------------------------------------+
| ``.``                 | Selects the current node.  This is mostly useful     |
|                       | at the beginning of the path, to indicate that it's  |
|                       | a relative path.                                     |
+-----------------------+------------------------------------------------------+
| ``//``                | Selects all subelements, on all levels beneath the   |
|                       | current  element.  For example, ``.//egg`` selects   |
|                       | all ``egg`` elements in the entire tree.             |
+-----------------------+------------------------------------------------------+
| ``..``                | Selects the parent element.  Returns ``None`` if the |
|                       | path attempts to reach the ancestors of the start    |
|                       | element (the element ``find`` was called on).        |
+-----------------------+------------------------------------------------------+
| ``[@attrib]``         | Selects all elements that have the given attribute.  |
+-----------------------+------------------------------------------------------+
| ``[@attrib='value']`` | Selects all elements for which the given attribute   |
|                       | has the given value.  The value cannot contain       |
|                       | quotes.                                              |
+-----------------------+------------------------------------------------------+
| ``[tag]``             | Selects all elements that have a child named         |
|                       | ``tag``.  Only immediate children are supported.     |
+-----------------------+------------------------------------------------------+
| ``[position]``        | Selects all elements that are located at the given   |
|                       | position.  The position can be either an integer     |
|                       | (1 is the first position), the expression ``last()`` |
|                       | (for the last position), or a position relative to   |
|                       | the last position (e.g. ``last()-1``).               |
+-----------------------+------------------------------------------------------+

Predicates (expressions within square brackets) must be preceded by a tag
name, an asterisk, or another predicate.  ``position`` predicates must be
preceded by a tag name.

Reference
---------

.. _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 sequence 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* can only use the default
   :class:`TreeBuilder` as a target.  Returns an :term:`iterator` providing
   ``(event, elem)`` pairs.

   Note that while :func:`iterparse` builds the tree incrementally, it issues
   blocking reads on *source* (or the file it names).  As such, it's unsuitable
   for asynchronous applications where blocking reads can't be made.  For fully
   asynchronous parsing, see :class:`IncrementalParser`.

   .. 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", *, \
                       short_empty_elements=True)

   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 (otherwise, a bytestring is generated).  *method*
   is either ``"xml"``, ``"html"`` or ``"text"`` (default is ``"xml"``).
   *short_empty_elements* has the same meaning as in :meth:`ElementTree.write`.
   Returns an (optionally) encoded string containing the XML data.

   .. versionadded:: 3.4
      The *short_empty_elements* parameter.


.. function:: tostringlist(element, encoding="us-ascii", method="xml", *, \
                           short_empty_elements=True)

   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 (otherwise, a bytestring is generated).  *method*
   is either ``"xml"``, ``"html"`` or ``"text"`` (default is ``"xml"``).
   *short_empty_elements* has the same meaning as in :meth:`ElementTree.write`.
   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

   .. versionadded:: 3.4
      The *short_empty_elements* parameter.


.. 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 element's internal list
      of subelements.  Raises :exc:`TypeError` if *subelement* is not an
      :class:`Element`.


   .. method:: extend(subelements)

      Appends *subelements* from a sequence object with zero or more elements.
      Raises :exc:`TypeError` if a subelement is not an :class:`Element`.

      .. versionadded:: 3.2


   .. method:: find(match, namespaces=None)

      Finds the first subelement matching *match*.  *match* may be a tag name
      or a :ref:`path <elementtree-xpath>`.  Returns an element instance
      or ``None``.  *namespaces* is an optional mapping from namespace prefix
      to full name.


   .. method:: findall(match, namespaces=None)

      Finds all matching subelements, by tag name or
      :ref:`path <elementtree-xpath>`.  Returns a list containing all matching
      elements in document order.  *namespaces* is an optional mapping from
      namespace prefix to full name.


   .. method:: findtext(match, default=None, namespaces=None)

      Finds text for the first subelement matching *match*.  *match* may be
      a tag name or a :ref:`path <elementtree-xpath>`.  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. *namespaces* is an optional mapping from namespace prefix
      to full name.


   .. 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, subelement)

      Inserts *subelement* at the given position in this element.  Raises
      :exc:`TypeError` if *subelement* is not an :class:`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, namespaces=None)

      Finds all matching subelements, by tag name or
      :ref:`path <elementtree-xpath>`.  Returns an iterable yielding all
      matching elements in document order. *namespaces* is an optional mapping
      from namespace prefix to full name.


      .. 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, namespaces=None)

      Same as :meth:`Element.find`, starting at the root of the tree.


   .. method:: findall(match, namespaces=None)

      Same as :meth:`Element.findall`, starting at the root of the tree.


   .. method:: findtext(match, default=None, namespaces=None)

      Same as :meth:`Element.findtext`, starting at the root of the tree.


   .. 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, namespaces=None)

      Same as :meth:`Element.iterfind`, starting at the root of the tree.

      .. 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 :class:`XMLParser` parser is used.  Returns the
      section root element.


   .. method:: write(file, encoding="us-ascii", xml_declaration=None, \
                     default_namespace=None, method="xml", *, \
                     short_empty_elements=True)

      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).
      *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"``).
      The keyword-only *short_empty_elements* parameter controls the formatting
      of elements that contain no content.  If *True* (the default), they are
      emitted as a single self-closed tag, otherwise they are emitted as a pair
      of start/end tags.

      The output is either a string (:class:`str`) or binary (:class:`bytes`).
      This is controlled by the *encoding* argument.  If *encoding* is
      ``"unicode"``, the output is a string; otherwise, it's binary.  Note that
      this may conflict with the type of *file* if it's an open
      :term:`file object`; make sure you do not try to write a string to a
      binary stream and vice versa.

   .. versionadded:: 3.4
      The *short_empty_elements* parameter.


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.


IncrementalParser Objects
^^^^^^^^^^^^^^^^^^^^^^^^^

.. class:: IncrementalParser(events=None, parser=None)

   An incremental, event-driven parser suitable for non-blocking applications.
   *events* is a sequence 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* can only use the default :class:`TreeBuilder` as a target.

   .. method:: data_received(data)

      Feed the given bytes data to the incremental parser.

   .. method:: eof_received()

      Signal the incremental parser that the data stream is terminated.

   .. method:: events()

      Iterate over the events which have been encountered in the data fed
      to the parser.  This method yields ``(event, elem)`` pairs, where
      *event* is a string representing the type of event (e.g. ``"end"``)
      and *elem* is the encountered :class:`Element` object.  Events
      provided in a previous call to :meth:`events` will not be yielded
      again.

   .. note::

      :class:`IncrementalParser` 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.

   .. versionadded:: 3.4


.. _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.  *element_factory*, when given,
   must be a callable accepting two positional arguments: a tag and
   a dict of attributes.  It is expected to return a new element instance.

   .. 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 :class:`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

Exceptions
^^^^^^^^^^

.. class:: ParseError

   XML parse error, raised by the various parsing methods in this module when
   parsing fails.  The string representation of an instance of this exception
   will contain a user-friendly error message.  In addition, it will have
   the following attributes available:

   .. attribute:: code

      A numeric error code from the expat parser. See the documentation of
      :mod:`xml.parsers.expat` for the list of error codes and their meanings.

   .. attribute:: position

      A tuple of *line*, *column* numbers, specifying where the error occurred.

.. 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.