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

New in version 2.5.

**Source code:** Lib/xml/etree/ElementTree.py

======================================================================

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.

Warning: The "xml.etree.ElementTree" module is not secure against
  maliciously constructed data.  If you need to parse untrusted or
  unauthenticated data see *XML vulnerabilities*.

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" constructor or the
"SubElement()" factory function.

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.

Changed in version 2.7: The ElementTree API is updated to 1.3.  For
more information, see Introducing ElementTree 1.3.


Tutorial
========

This is a short tutorial for using "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 - "ElementTree" represents the whole XML document as a tree,
and "Element" represents a single node in this tree.  Interactions
with the whole document (reading and writing to/from files) are
usually done on the "ElementTree" level.  Interactions with a single
XML element and its sub-elements are done on the "Element" level.


Parsing XML
-----------

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

   <?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 have a number of ways to import the data.  Reading the file from
disk:

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

Reading the data from a string:

   root = ET.fromstring(country_data_as_string)

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

As an "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'


Finding interesting elements
----------------------------

"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, "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'}

"Element.findall()" finds only elements with a tag which are direct
children of the current element.  "Element.find()" finds the *first*
child with a particular tag, and "Element.text" accesses the element's
text content.  "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 *XPath*.


Modifying an XML File
---------------------

"ElementTree" provides a simple way to build XML documents and write
them to files. The "ElementTree.write()" method serves this purpose.

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

   <?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 "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:

   <?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 "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.


XPath support
=============

This module provides limited support for XPath expressions 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
*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
----------------------

+-------------------------+--------------------------------------------------------+
| Syntax                  | Meaning                                                |
+=========================+========================================================+
| "tag"                   | Selects all child elements with the given tag. For     |
|                         | example, "spam" selects all child elements named       |
|                         | "spam", and "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.                            |
+-------------------------+--------------------------------------------------------+
| "[@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
=========


Functions
---------

xml.etree.ElementTree.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.

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.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.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 "XMLParser" parser is used.  Returns an "Element"
   instance.

   New in version 2.7.

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=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
   file object containing XML data.  *events* is a list of events to
   report back.  If omitted, only "end" events are reported.  *parser*
   is an optional parser instance.  If not given, the standard
   "XMLParser" parser is used.  *parser* is not supported by
   "cElementTree". 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=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 "XMLParser" parser is used.
   Returns an "ElementTree" instance.

xml.etree.ElementTree.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.

xml.etree.ElementTree.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.

   New in version 2.7.

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
   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.

xml.etree.ElementTree.tostring(element, encoding="us-ascii", method="xml")

   Generates a string representation of an XML element, including all
   subelements.  *element* is an "Element" instance.  *encoding* [1]
   is the output encoding (default is US-ASCII).  *method* is either
   ""xml"", ""html"" or ""text"" (default is ""xml"").  Returns an
   encoded string containing the XML data.

xml.etree.ElementTree.tostringlist(element, encoding="us-ascii", method="xml")

   Generates a string representation of an XML element, including all
   subelements.  *element* is an "Element" instance.  *encoding* [1]
   is the output encoding (default is US-ASCII).   *method* is either
   ""xml"", ""html"" or ""text"" (default is ""xml"").  Returns a list
   of encoded strings containing the XML data.  It does not guarantee
   any specific sequence, except that """.join(tostringlist(element))
   == tostring(element)".

   New in version 2.7.

xml.etree.ElementTree.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 "XMLParser" parser is used.  Returns an
   "Element" instance.

xml.etree.ElementTree.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 "XMLParser" parser is used.
   Returns a tuple containing an "Element" instance and a dictionary.


Element Objects
---------------

class class xml.etree.ElementTree.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.

   tag

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

   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.

   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.

   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.

   clear()

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

   get(key, default=None)

      Gets the element attribute named *key*.

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

   items()

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

   keys()

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

   set(key, value)

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

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

   append(subelement)

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

   extend(subelements)

      Appends *subelements* from a sequence object with zero or more
      elements. Raises "AssertionError" if a subelement is not a valid
      object.

      New in version 2.7.

   find(match)

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

   findall(match)

      Finds all matching subelements, by tag name or path.  Returns a
      list containing all matching elements in document order.

   findtext(match, default=None)

      Finds text for the first subelement matching *match*.  *match*
      may be a tag name or path.  Returns the text content of the
      first matching element, or *default* if no element was found.
      Note that if the matching element has no text content an empty
      string is returned.

   getchildren()

      Deprecated since version 2.7: Use "list(elem)" or iteration.

   getiterator(tag=None)

      Deprecated since version 2.7: Use method "Element.iter()"
      instead.

   insert(index, element)

      Inserts a subelement at the given position in this element.

   iter(tag=None)

      Creates a tree *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.

      New in version 2.7.

   iterfind(match)

      Finds all matching subelements, by tag name or path.  Returns an
      iterable yielding all matching elements in document order.

      New in version 2.7.

   itertext()

      Creates a text iterator.  The iterator loops over this element
      and all subelements, in document order, and returns all inner
      text.

      New in version 2.7.

   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.

   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.

   "Element" objects also support the following sequence type methods
   for working with subelements: "__delitem__()", "__getitem__()",
   "__setitem__()", "__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 Objects
-------------------

class class xml.etree.ElementTree.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.

   _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(match)

      Same as "Element.find()", starting at the root of the tree.

   findall(match)

      Same as "Element.findall()", starting at the root of the tree.

   findtext(match, default=None)

      Same as "Element.findtext()", starting at the root of the tree.

   getiterator(tag=None)

      Deprecated since version 2.7: Use method "ElementTree.iter()"
      instead.

   getroot()

      Returns the root element for this tree.

   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)

   iterfind(match)

      Finds all matching subelements, by tag name or path.  Same as
      getroot().iterfind(match). Returns an iterable yielding all
      matching elements in document order.

      New in version 2.7.

   parse(source, parser=None)

      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 XMLParser parser is used.
      Returns the section root element.

   write(file, encoding="us-ascii", xml_declaration=None, default_namespace=None, method="xml")

      Writes the element tree to a file, as XML.  *file* is a file
      name, or a 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 (default is None).  *default_namespace* sets the
      default XML namespace (for "xmlns").  *method* is either
      ""xml"", ""html"" or ""text"" (default is ""xml"").  Returns an
      encoded string.

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

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

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

   >>> from xml.etree.ElementTree import ElementTree
   >>> tree = ElementTree()
   >>> tree.parse("index.xhtml")
   <Element 'html' at 0xb77e6fac>
   >>> p = tree.find("body/p")     # Finds first occurrence of tag p in body
   >>> p
   <Element 'p' at 0xb77ec26c>
   >>> links = list(p.iter("a"))   # Returns list of all links
   >>> links
   [<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
   >>> for i in links:             # Iterates through all found links
   ...     i.attrib["target"] = "blank"
   >>> tree.write("output.xhtml")


QName Objects
-------------

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


TreeBuilder Objects
-------------------

class class xml.etree.ElementTree.TreeBuilder(element_factory=None)

   Generic element structure builder.  This builder converts a
   sequence of start, data, and end method calls to a well-formed
   element structure.  You can use this class to build an element
   structure using a custom XML parser, or a parser for some other
   XML-like format.  The *element_factory* is called to create new
   "Element" instances when given.

   close()

      Flushes the builder 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 a bytestring, or a Unicode string.

   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.

   In addition, a custom "TreeBuilder" object can provide the
   following 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
      "TreeBuilder" class.

      New in version 2.7.


XMLParser Objects
-----------------

class class xml.etree.ElementTree.XMLParser(html=0, target=None, encoding=None)

   "Element" structure builder for XML source data, based on the expat
   parser.  *html* are predefined HTML entities.  This flag is not
   supported by the current implementation.  *target* is the target
   object.  If omitted, the builder uses an instance of the standard
   TreeBuilder class.  *encoding* [1] is optional.  If given, the
   value overrides the encoding specified in the XML file.

   close()

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

   doctype(name, pubid, system)

      Deprecated since version 2.7: Define the "TreeBuilder.doctype()"
      method on a custom TreeBuilder target.

   feed(data)

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

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

-[ 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 /character-
    sets.xhtml.
