text: #
  # ElementTree
  # $Id: ElementTree.py 3440 2008-07-18 14:45:01Z fredrik $
  #
  # light-weight XML support for Python 2.3 and later.
  #
  # history (since 1.2.6):
  # 2005-11-12 fl   added tostringlist/fromstringlist helpers
  # 2006-07-05 fl   merged in selected changes from the 1.3 sandbox
  # 2006-07-05 fl   removed support for 2.1 and earlier
  # 2007-06-21 fl   added deprecation/future warnings
  # 2007-08-25 fl   added doctype hook, added parser version attribute etc
  # 2007-08-26 fl   added new serializer code (better namespace handling, etc)
  # 2007-08-27 fl   warn for broken /tag searches on tree level
  # 2007-09-02 fl   added html/text methods to serializer (experimental)
  # 2007-09-05 fl   added method argument to tostring/tostringlist
  # 2007-09-06 fl   improved error handling
  # 2007-09-13 fl   added itertext, iterfind; assorted cleanups
  # 2007-12-15 fl   added C14N hooks, copy method (experimental)
  #
  # Copyright (c) 1999-2008 by Fredrik Lundh.  All rights reserved.
  #
  # fredrik@pythonware.com
  # http://www.pythonware.com
  #
  # --------------------------------------------------------------------
  # The ElementTree toolkit is
  #
  # Copyright (c) 1999-2008 by Fredrik Lundh
  #
  # By obtaining, using, and/or copying this software and/or its
  # associated documentation, you agree that you have read, understood,
  # and will comply with the following terms and conditions:
  #
  # Permission to use, copy, modify, and distribute this software and
  # its associated documentation for any purpose and without fee is
  # hereby granted, provided that the above copyright notice appears in
  # all copies, and that both that copyright notice and this permission
  # notice appear in supporting documentation, and that the name of
  # Secret Labs AB or the author not be used in advertising or publicity
  # pertaining to distribution of the software without specific, written
  # prior permission.
  #
  # SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
  # TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-
  # ABILITY AND FITNESS.  IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR
  # BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
  # DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
  # WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  # ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
  # OF THIS SOFTWARE.
  # --------------------------------------------------------------------
  
  # Licensed to PSF under a Contributor Agreement.
  # See http://www.python.org/psf/license for licensing details.
  
  __all__ = [
      # public symbols
      "Comment",
      "dump",
      "Element", "ElementTree",
      "fromstring", "fromstringlist",
      "iselement", "iterparse",
      "parse", "ParseError",
      "PI", "ProcessingInstruction",
      "QName",
      "SubElement",
      "tostring", "tostringlist",
      "TreeBuilder",
      "VERSION",
      "XML",
      "XMLParser", "XMLTreeBuilder",
      ]
  
  VERSION = "1.3.0"
  
  ##
  # The <b>Element</b> 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.
  # <p>
  # Each element has a number of properties associated with it:
  # <ul>
  # <li>a <i>tag</i>. This is a string identifying what kind of data
  # this element represents (the element type, in other words).</li>
  # <li>a number of <i>attributes</i>, stored in a Python dictionary.</li>
  # <li>a <i>text</i> string.</li>
  # <li>an optional <i>tail</i> string.</li>
  # <li>a number of <i>child elements</i>, stored in a Python sequence</li>
  # </ul>
  #
  # To create an element instance, use the {@link #Element} constructor
  # or the {@link #SubElement} factory function.
  # <p>
  # The {@link #ElementTree} class can be used to wrap an element
  # structure, and convert it from and to XML.
  ##
  
  import sys
  import re
  import warnings
  
  
  class _SimpleElementPath(object):
      # emulate pre-1.2 find/findtext/findall behaviour
      def find(self, element, tag, namespaces=None):
          for elem in element:
              if elem.tag == tag:
                  return elem
          return None
      def findtext(self, element, tag, default=None, namespaces=None):
          elem = self.find(element, tag)
          if elem is None:
              return default
          return elem.text or ""
      def iterfind(self, element, tag, namespaces=None):
          if tag[:3] == ".//":
              for elem in element.iter(tag[3:]):
                  yield elem
          for elem in element:
              if elem.tag == tag:
                  yield elem
      def findall(self, element, tag, namespaces=None):
          return list(self.iterfind(element, tag, namespaces))
  
  try:
      from . import ElementPath
  except ImportError:
      ElementPath = _SimpleElementPath()
  
  ##
  # Parser error.  This is a subclass of <b>SyntaxError</b>.
  # <p>
  # In addition to the exception value, an exception instance contains a
  # specific exception code in the <b>code</b> attribute, and the line and
  # column of the error in the <b>position</b> attribute.
  
  class ParseError(SyntaxError):
      pass
  
  # --------------------------------------------------------------------
  
  ##
  # Checks if an object appears to be a valid element object.
  #
  # @param An element instance.
  # @return A true value if this is an element object.
  # @defreturn flag
  
  def iselement(element):
      # FIXME: not sure about this; might be a better idea to look
      # for tag/attrib/text attributes
      return isinstance(element, Element) or hasattr(element, "tag")
  
  ##
  # Element class.  This class defines the Element interface, and
  # provides a reference implementation of this interface.
  # <p>
  # The element name, attribute names, and attribute values can be
  # either ASCII strings (ordinary Python strings containing only 7-bit
  # ASCII characters) or Unicode strings.
  #
  # @param tag The element name.
  # @param attrib An optional dictionary, containing element attributes.
  # @param **extra Additional attributes, given as keyword arguments.
  # @see Element
  # @see SubElement
  # @see Comment
  # @see ProcessingInstruction
  
  class Element(object):
      # <tag attrib>text<child/>...</tag>tail
  
      ##
      # (Attribute) Element tag.
  
      tag = None
  
      ##
      # (Attribute) Element attribute dictionary.  Where possible, use
      # {@link #Element.get},
      # {@link #Element.set},
      # {@link #Element.keys}, and
      # {@link #Element.items} to access
      # element attributes.
  
      attrib = None
  
      ##
      # (Attribute) Text before first subelement.  This is either a
      # string or the value None.  Note that if there was no text, this
      # attribute may be either None or an empty string, depending on
      # the parser.
  
      text = None
  
      ##
      # (Attribute) Text after this element's end tag, but before the
      # next sibling element's start tag.  This is either a string or
      # the value None.  Note that if there was no text, this attribute
      # may be either None or an empty string, depending on the parser.
  
      tail = None # text after end tag, if any
  
      # constructor
  
      def __init__(self, tag, attrib={}, **extra):
          attrib = attrib.copy()
          attrib.update(extra)
          self.tag = tag
          self.attrib = attrib
          self._children = []
  
      def __repr__(self):
          return "<Element %s at 0x%x>" % (repr(self.tag), id(self))
  
      ##
      # Creates a new element object of the same type as this element.
      #
      # @param tag Element tag.
      # @param attrib Element attributes, given as a dictionary.
      # @return A new element instance.
  
      def makeelement(self, tag, attrib):
          return self.__class__(tag, attrib)
  
      ##
      # (Experimental) Copies the current element.  This creates a
      # shallow copy; subelements will be shared with the original tree.
      #
      # @return A new element instance.
  
      def copy(self):
          elem = self.makeelement(self.tag, self.attrib)
          elem.text = self.text
          elem.tail = self.tail
          elem[:] = self
          return elem
  
      ##
      # Returns the number of subelements.  Note that this only counts
      # full elements; to check if there's any content in an element, you
      # have to check both the length and the <b>text</b> attribute.
      #
      # @return The number of subelements.
  
      def __len__(self):
          return len(self._children)
  
      def __nonzero__(self):
          warnings.warn(
              "The behavior of this method will change in future versions.  "
              "Use specific 'len(elem)' or 'elem is not None' test instead.",
              FutureWarning, stacklevel=2
              )
          return len(self._children) != 0 # emulate old behaviour, for now
  
      ##
      # Returns the given subelement, by index.
      #
      # @param index What subelement to return.
      # @return The given subelement.
      # @exception IndexError If the given element does not exist.
  
      def __getitem__(self, index):
          return self._children[index]
  
      ##
      # Replaces the given subelement, by index.
      #
      # @param index What subelement to replace.
      # @param element The new element value.
      # @exception IndexError If the given element does not exist.
  
      def __setitem__(self, index, element):
          # if isinstance(index, slice):
          #     for elt in element:
          #         assert iselement(elt)
          # else:
          #     assert iselement(element)
          self._children[index] = element
  
      ##
      # Deletes the given subelement, by index.
      #
      # @param index What subelement to delete.
      # @exception IndexError If the given element does not exist.
  
      def __delitem__(self, index):
          del self._children[index]
  
      ##
      # Adds a subelement to the end of this element.  In document order,
      # the new element will appear after the last existing subelement (or
      # directly after the text, if it's the first subelement), but before
      # the end tag for this element.
      #
      # @param element The element to add.
  
      def append(self, element):
          # assert iselement(element)
          self._children.append(element)
  
      ##
      # Appends subelements from a sequence.
      #
      # @param elements A sequence object with zero or more elements.
      # @since 1.3
  
      def extend(self, elements):
          # for element in elements:
          #     assert iselement(element)
          self._children.extend(elements)
  
      ##
      # Inserts a subelement at the given position in this element.
      #
      # @param index Where to insert the new subelement.
  
      def insert(self, index, element):
          # assert iselement(element)
          self._children.insert(index, element)
  
      ##
      # Removes a matching subelement.  Unlike the <b>find</b> methods,
      # this method compares elements based on identity, not on tag
      # value or contents.  To remove subelements by other means, the
      # easiest way is often to use a list comprehension to select what
      # elements to keep, and use slice assignment to update the parent
      # element.
      #
      # @param element What element to remove.
      # @exception ValueError If a matching element could not be found.
  
      def remove(self, element):
          # assert iselement(element)
          self._children.remove(element)
  
      ##
      # (Deprecated) Returns all subelements.  The elements are returned
      # in document order.
      #
      # @return A list of subelements.
      # @defreturn list of Element instances
  
      def getchildren(self):
          warnings.warn(
              "This method will be removed in future versions.  "
              "Use 'list(elem)' or iteration over elem instead.",
              DeprecationWarning, stacklevel=2
              )
          return self._children
  
      ##
      # Finds the first matching subelement, by tag name or path.
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return The first matching element, or None if no element was found.
      # @defreturn Element or None
  
      def find(self, path, namespaces=None):
          return ElementPath.find(self, path, namespaces)
  
      ##
      # Finds text for the first matching subelement, by tag name or path.
      #
      # @param path What element to look for.
      # @param default What to return if the element was not found.
      # @keyparam namespaces Optional namespace prefix map.
      # @return The text content of the first matching element, or the
      #     default value no element was found.  Note that if the element
      #     is found, but has no text content, this method returns an
      #     empty string.
      # @defreturn string
  
      def findtext(self, path, default=None, namespaces=None):
          return ElementPath.findtext(self, path, default, namespaces)
  
      ##
      # Finds all matching subelements, by tag name or path.
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return A list or other sequence containing all matching elements,
      #    in document order.
      # @defreturn list of Element instances
  
      def findall(self, path, namespaces=None):
          return ElementPath.findall(self, path, namespaces)
  
      ##
      # Finds all matching subelements, by tag name or path.
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return An iterator or sequence containing all matching elements,
      #    in document order.
      # @defreturn a generated sequence of Element instances
  
      def iterfind(self, path, namespaces=None):
          return ElementPath.iterfind(self, path, namespaces)
  
      ##
      # Resets an element.  This function removes all subelements, clears
      # all attributes, and sets the <b>text</b> and <b>tail</b> attributes
      # to None.
  
      def clear(self):
          self.attrib.clear()
          self._children = []
          self.text = self.tail = None
  
      ##
      # Gets an element attribute.  Equivalent to <b>attrib.get</b>, but
      # some implementations may handle this a bit more efficiently.
      #
      # @param key What attribute to look for.
      # @param default What to return if the attribute was not found.
      # @return The attribute value, or the default value, if the
      #     attribute was not found.
      # @defreturn string or None
  
      def get(self, key, default=None):
          return self.attrib.get(key, default)
  
      ##
      # Sets an element attribute.  Equivalent to <b>attrib[key] = value</b>,
      # but some implementations may handle this a bit more efficiently.
      #
      # @param key What attribute to set.
      # @param value The attribute value.
  
      def set(self, key, value):
          self.attrib[key] = value
  
      ##
      # Gets a list of attribute names.  The names are returned in an
      # arbitrary order (just like for an ordinary Python dictionary).
      # Equivalent to <b>attrib.keys()</b>.
      #
      # @return A list of element attribute names.
      # @defreturn list of strings
  
      def keys(self):
          return self.attrib.keys()
  
      ##
      # Gets element attributes, as a sequence.  The attributes are
      # returned in an arbitrary order.  Equivalent to <b>attrib.items()</b>.
      #
      # @return A list of (name, value) tuples for all attributes.
      # @defreturn list of (string, string) tuples
  
      def items(self):
          return self.attrib.items()
  
      ##
      # Creates a tree iterator.  The iterator loops over this element
      # and all subelements, in document order, and returns all elements
      # with a matching tag.
      # <p>
      # If the tree structure is modified during iteration, new or removed
      # elements may or may not be included.  To get a stable set, use the
      # list() function on the iterator, and loop over the resulting list.
      #
      # @param tag What tags to look for (default is to return all elements).
      # @return An iterator containing all the matching elements.
      # @defreturn iterator
  
      def iter(self, tag=None):
          if tag == "*":
              tag = None
          if tag is None or self.tag == tag:
              yield self
          for e in self._children:
              for e in e.iter(tag):
                  yield e
  
      # compatibility
      def getiterator(self, tag=None):
          # Change for a DeprecationWarning in 1.4
          warnings.warn(
              "This method will be removed in future versions.  "
              "Use 'elem.iter()' or 'list(elem.iter())' instead.",
              PendingDeprecationWarning, stacklevel=2
          )
          return list(self.iter(tag))
  
      ##
      # Creates a text iterator.  The iterator loops over this element
      # and all subelements, in document order, and returns all inner
      # text.
      #
      # @return An iterator containing all inner text.
      # @defreturn iterator
  
      def itertext(self):
          tag = self.tag
          if not isinstance(tag, basestring) and tag is not None:
              return
          if self.text:
              yield self.text
          for e in self:
              for s in e.itertext():
                  yield s
              if e.tail:
                  yield e.tail
  
  # compatibility
  _Element = _ElementInterface = Element
  
  ##
  # Subelement factory.  This function creates an element instance, and
  # appends it to an existing element.
  # <p>
  # The element name, attribute names, and attribute values can be
  # either 8-bit ASCII strings or Unicode strings.
  #
  # @param parent The parent element.
  # @param tag The subelement name.
  # @param attrib An optional dictionary, containing element attributes.
  # @param **extra Additional attributes, given as keyword arguments.
  # @return An element instance.
  # @defreturn Element
  
  def SubElement(parent, tag, attrib={}, **extra):
      attrib = attrib.copy()
      attrib.update(extra)
      element = parent.makeelement(tag, attrib)
      parent.append(element)
      return element
  
  ##
  # Comment element factory.  This factory function creates a special
  # element that will be serialized as an XML comment by the standard
  # serializer.
  # <p>
  # The comment string can be either an 8-bit ASCII string or a Unicode
  # string.
  #
  # @param text A string containing the comment string.
  # @return An element instance, representing a comment.
  # @defreturn Element
  
  def Comment(text=None):
      element = Element(Comment)
      element.text = text
      return element
  
  ##
  # PI element factory.  This factory function creates a special element
  # that will be serialized as an XML processing instruction by the standard
  # serializer.
  #
  # @param target A string containing the PI target.
  # @param text A string containing the PI contents, if any.
  # @return An element instance, representing a PI.
  # @defreturn Element
  
  def ProcessingInstruction(target, text=None):
      element = Element(ProcessingInstruction)
      element.text = target
      if text:
          element.text = element.text + " " + text
      return element
  
  PI = ProcessingInstruction
  
  ##
  # QName wrapper.  This can be used to wrap a QName attribute value, in
  # order to get proper namespace handling on output.
  #
  # @param text A string containing the QName value, in the form {uri}local,
  #     or, if the tag argument is given, the URI part of a QName.
  # @param tag Optional tag.  If given, the first argument is interpreted as
  #     an URI, and this argument is interpreted as a local name.
  # @return An opaque object, representing the QName.
  
  class QName(object):
      def __init__(self, text_or_uri, tag=None):
          if tag:
              text_or_uri = "{%s}%s" % (text_or_uri, tag)
          self.text = text_or_uri
      def __str__(self):
          return self.text
      def __hash__(self):
          return hash(self.text)
      def __cmp__(self, other):
          if isinstance(other, QName):
              return cmp(self.text, other.text)
          return cmp(self.text, other)
  
  # --------------------------------------------------------------------
  
  ##
  # ElementTree wrapper class.  This class represents an entire element
  # hierarchy, and adds some extra support for serialization to and from
  # standard XML.
  #
  # @param element Optional root element.
  # @keyparam file Optional file handle or file name.  If given, the
  #     tree is initialized with the contents of this XML file.
  
  class ElementTree(object):
  
      def __init__(self, element=None, file=None):
          # assert element is None or iselement(element)
          self._root = element # first node
          if file:
              self.parse(file)
  
      ##
      # Gets the root element for this tree.
      #
      # @return An element instance.
      # @defreturn Element
  
      def getroot(self):
          return self._root
  
      ##
      # 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.
      #
      # @param element An element instance.
  
      def _setroot(self, element):
          # assert iselement(element)
          self._root = element
  
      ##
      # Loads an external XML document into this element tree.
      #
      # @param source A file name or file object.  If a file object is
      #     given, it only has to implement a <b>read(n)</b> method.
      # @keyparam parser An optional parser instance.  If not given, the
      #     standard {@link XMLParser} parser is used.
      # @return The document root element.
      # @defreturn Element
      # @exception ParseError If the parser fails to parse the document.
  
      def parse(self, source, parser=None):
          close_source = False
          if not hasattr(source, "read"):
              source = open(source, "rb")
              close_source = True
          try:
              if not parser:
                  parser = XMLParser(target=TreeBuilder())
              while 1:
                  data = source.read(65536)
                  if not data:
                      break
                  parser.feed(data)
              self._root = parser.close()
              return self._root
          finally:
              if close_source:
                  source.close()
  
      ##
      # Creates a tree iterator for the root element.  The iterator loops
      # over all elements in this tree, in document order.
      #
      # @param tag What tags to look for (default is to return all elements)
      # @return An iterator.
      # @defreturn iterator
  
      def iter(self, tag=None):
          # assert self._root is not None
          return self._root.iter(tag)
  
      # compatibility
      def getiterator(self, tag=None):
          # Change for a DeprecationWarning in 1.4
          warnings.warn(
              "This method will be removed in future versions.  "
              "Use 'tree.iter()' or 'list(tree.iter())' instead.",
              PendingDeprecationWarning, stacklevel=2
          )
          return list(self.iter(tag))
  
      ##
      # Same as getroot().find(path), starting at the root of the
      # tree.
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return The first matching element, or None if no element was found.
      # @defreturn Element or None
  
      def find(self, path, namespaces=None):
          # assert self._root is not None
          if path[:1] == "/":
              path = "." + path
              warnings.warn(
                  "This search is broken in 1.3 and earlier, and will be "
                  "fixed in a future version.  If you rely on the current "
                  "behaviour, change it to %r" % path,
                  FutureWarning, stacklevel=2
                  )
          return self._root.find(path, namespaces)
  
      ##
      # Same as getroot().findtext(path), starting at the root of the tree.
      #
      # @param path What element to look for.
      # @param default What to return if the element was not found.
      # @keyparam namespaces Optional namespace prefix map.
      # @return The text content of the first matching element, or the
      #     default value no element was found.  Note that if the element
      #     is found, but has no text content, this method returns an
      #     empty string.
      # @defreturn string
  
      def findtext(self, path, default=None, namespaces=None):
          # assert self._root is not None
          if path[:1] == "/":
              path = "." + path
              warnings.warn(
                  "This search is broken in 1.3 and earlier, and will be "
                  "fixed in a future version.  If you rely on the current "
                  "behaviour, change it to %r" % path,
                  FutureWarning, stacklevel=2
                  )
          return self._root.findtext(path, default, namespaces)
  
      ##
      # Same as getroot().findall(path), starting at the root of the tree.
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return A list or iterator containing all matching elements,
      #    in document order.
      # @defreturn list of Element instances
  
      def findall(self, path, namespaces=None):
          # assert self._root is not None
          if path[:1] == "/":
              path = "." + path
              warnings.warn(
                  "This search is broken in 1.3 and earlier, and will be "
                  "fixed in a future version.  If you rely on the current "
                  "behaviour, change it to %r" % path,
                  FutureWarning, stacklevel=2
                  )
          return self._root.findall(path, namespaces)
  
      ##
      # Finds all matching subelements, by tag name or path.
      # Same as getroot().iterfind(path).
      #
      # @param path What element to look for.
      # @keyparam namespaces Optional namespace prefix map.
      # @return An iterator or sequence containing all matching elements,
      #    in document order.
      # @defreturn a generated sequence of Element instances
  
      def iterfind(self, path, namespaces=None):
          # assert self._root is not None
          if path[:1] == "/":
              path = "." + path
              warnings.warn(
                  "This search is broken in 1.3 and earlier, and will be "
                  "fixed in a future version.  If you rely on the current "
                  "behaviour, change it to %r" % path,
                  FutureWarning, stacklevel=2
                  )
          return self._root.iterfind(path, namespaces)
  
      ##
      # Writes the element tree to a file, as XML.
      #
      # @def write(file, **options)
      # @param file A file name, or a file object opened for writing.
      # @param **options Options, given as keyword arguments.
      # @keyparam encoding Optional output encoding (default is US-ASCII).
      # @keyparam 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.  None is default.
      # @keyparam default_namespace Sets the default XML namespace (for "xmlns").
      # @keyparam method Optional output method ("xml", "html", "text" or
      #     "c14n"; default is "xml").
  
      def write(self, file_or_filename,
                # keyword arguments
                encoding=None,
                xml_declaration=None,
                default_namespace=None,
                method=None):
          # assert self._root is not None
          if not method:
              method = "xml"
          elif method not in _serialize:
              # FIXME: raise an ImportError for c14n if ElementC14N is missing?
              raise ValueError("unknown method %r" % method)
          if hasattr(file_or_filename, "write"):
              file = file_or_filename
          else:
              file = open(file_or_filename, "wb")
          try:
              write = file.write
              if not encoding:
                  if method == "c14n":
                      encoding = "utf-8"
                  else:
                      encoding = "us-ascii"
              elif xml_declaration or (xml_declaration is None and
                                       encoding not in ("utf-8", "us-ascii")):
                  if method == "xml":
                      write("<?xml version='1.0' encoding='%s'?>\n" % encoding)
              if method == "text":
                  _serialize_text(write, self._root, encoding)
              else:
                  qnames, namespaces = _namespaces(
                      self._root, encoding, default_namespace
                      )
                  serialize = _serialize[method]
                  serialize(write, self._root, encoding, qnames, namespaces)
          finally:
              if file_or_filename is not file:
                  file.close()
  
      def write_c14n(self, file):
          # lxml.etree compatibility.  use output method instead
          return self.write(file, method="c14n")
  
  # --------------------------------------------------------------------
  # serialization support
  
  def _namespaces(elem, encoding, default_namespace=None):
      # identify namespaces used in this tree
  
      # maps qnames to *encoded* prefix:local names
      qnames = {None: None}
  
      # maps uri:s to prefixes
      namespaces = {}
      if default_namespace:
          namespaces[default_namespace] = ""
  
      def encode(text):
          return text.encode(encoding)
  
      def add_qname(qname):
          # calculate serialized qname representation
          try:
              if qname[:1] == "{":
                  uri, tag = qname[1:].rsplit("}", 1)
                  prefix = namespaces.get(uri)
                  if prefix is None:
                      prefix = _namespace_map.get(uri)
                      if prefix is None:
                          prefix = "ns%d" % len(namespaces)
                      if prefix != "xml":
                          namespaces[uri] = prefix
                  if prefix:
                      qnames[qname] = encode("%s:%s" % (prefix, tag))
                  else:
                      qnames[qname] = encode(tag) # default element
              else:
                  if default_namespace:
                      # FIXME: can this be handled in XML 1.0?
                      raise ValueError(
                          "cannot use non-qualified names with "
                          "default_namespace option"
                          )
                  qnames[qname] = encode(qname)
          except TypeError:
              _raise_serialization_error(qname)
  
      # populate qname and namespaces table
      try:
          iterate = elem.iter
      except AttributeError:
          iterate = elem.getiterator # cET compatibility
      for elem in iterate():
          tag = elem.tag
          if isinstance(tag, QName):
              if tag.text not in qnames:
                  add_qname(tag.text)
          elif isinstance(tag, basestring):
              if tag not in qnames:
                  add_qname(tag)
          elif tag is not None and tag is not Comment and tag is not PI:
              _raise_serialization_error(tag)
          for key, value in elem.items():
              if isinstance(key, QName):
                  key = key.text
              if key not in qnames:
                  add_qname(key)
              if isinstance(value, QName) and value.text not in qnames:
                  add_qname(value.text)
          text = elem.text
          if isinstance(text, QName) and text.text not in qnames:
              add_qname(text.text)
      return qnames, namespaces
  
  def _serialize_xml(write, elem, encoding, qnames, namespaces):
      tag = elem.tag
      text = elem.text
      if tag is Comment:
          write("<!--%s-->" % _encode(text, encoding))
      elif tag is ProcessingInstruction:
          write("<?%s?>" % _encode(text, encoding))
      else:
          tag = qnames[tag]
          if tag is None:
              if text:
                  write(_escape_cdata(text, encoding))
              for e in elem:
                  _serialize_xml(write, e, encoding, qnames, None)
          else:
              write("<" + tag)
              items = elem.items()
              if items or namespaces:
                  if namespaces:
                      for v, k in sorted(namespaces.items(),
                                         key=lambda x: x[1]):  # sort on prefix
                          if k:
                              k = ":" + k
                          write(" xmlns%s=\"%s\"" % (
                              k.encode(encoding),
                              _escape_attrib(v, encoding)
                              ))
                  for k, v in sorted(items):  # lexical order
                      if isinstance(k, QName):
                          k = k.text
                      if isinstance(v, QName):
                          v = qnames[v.text]
                      else:
                          v = _escape_attrib(v, encoding)
                      write(" %s=\"%s\"" % (qnames[k], v))
              if text or len(elem):
                  write(">")
                  if text:
                      write(_escape_cdata(text, encoding))
                  for e in elem:
                      _serialize_xml(write, e, encoding, qnames, None)
                  write("</" + tag + ">")
              else:
                  write(" />")
      if elem.tail:
          write(_escape_cdata(elem.tail, encoding))
  
  HTML_EMPTY = ("area", "base", "basefont", "br", "col", "frame", "hr",
                "img", "input", "isindex", "link", "meta", "param")
  
  try:
      HTML_EMPTY = set(HTML_EMPTY)
  except NameError:
      pass
  
  def _serialize_html(write, elem, encoding, qnames, namespaces):
      tag = elem.tag
      text = elem.text
      if tag is Comment:
          write("<!--%s-->" % _escape_cdata(text, encoding))
      elif tag is ProcessingInstruction:
          write("<?%s?>" % _escape_cdata(text, encoding))
      else:
          tag = qnames[tag]
          if tag is None:
              if text:
                  write(_escape_cdata(text, encoding))
              for e in elem:
                  _serialize_html(write, e, encoding, qnames, None)
          else:
              write("<" + tag)
              items = elem.items()
              if items or namespaces:
                  if namespaces:
                      for v, k in sorted(namespaces.items(),
                                         key=lambda x: x[1]):  # sort on prefix
                          if k:
                              k = ":" + k
                          write(" xmlns%s=\"%s\"" % (
                              k.encode(encoding),
                              _escape_attrib(v, encoding)
                              ))
                  for k, v in sorted(items):  # lexical order
                      if isinstance(k, QName):
                          k = k.text
                      if isinstance(v, QName):
                          v = qnames[v.text]
                      else:
                          v = _escape_attrib_html(v, encoding)
                      # FIXME: handle boolean attributes
                      write(" %s=\"%s\"" % (qnames[k], v))
              write(">")
              ltag = tag.lower()
              if text:
                  if ltag == "script" or ltag == "style":
                      write(_encode(text, encoding))
                  else:
                      write(_escape_cdata(text, encoding))
              for e in elem:
                  _serialize_html(write, e, encoding, qnames, None)
              if ltag not in HTML_EMPTY:
                  write("</" + tag + ">")
      if elem.tail:
          write(_escape_cdata(elem.tail, encoding))
  
  def _serialize_text(write, elem, encoding):
      for part in elem.itertext():
          write(part.encode(encoding))
      if elem.tail:
          write(elem.tail.encode(encoding))
  
  _serialize = {
      "xml": _serialize_xml,
      "html": _serialize_html,
      "text": _serialize_text,
  # this optional method is imported at the end of the module
  #   "c14n": _serialize_c14n,
  }
  
  ##
  # Registers a namespace prefix.  The registry is global, and any
  # existing mapping for either the given prefix or the namespace URI
  # will be removed.
  #
  # @param prefix Namespace prefix.
  # @param uri Namespace uri.  Tags and attributes in this namespace
  #     will be serialized with the given prefix, if at all possible.
  # @exception ValueError If the prefix is reserved, or is otherwise
  #     invalid.
  
  def register_namespace(prefix, uri):
      if re.match("ns\d+$", prefix):
          raise ValueError("Prefix format reserved for internal use")
      for k, v in _namespace_map.items():
          if k == uri or v == prefix:
              del _namespace_map[k]
      _namespace_map[uri] = prefix
  
  _namespace_map = {
      # "well-known" namespace prefixes
      "http://www.w3.org/XML/1998/namespace": "xml",
      "http://www.w3.org/1999/xhtml": "html",
      "http://www.w3.org/1999/02/22-rdf-syntax-ns#": "rdf",
      "http://schemas.xmlsoap.org/wsdl/": "wsdl",
      # xml schema
      "http://www.w3.org/2001/XMLSchema": "xs",
      "http://www.w3.org/2001/XMLSchema-instance": "xsi",
      # dublin core
      "http://purl.org/dc/elements/1.1/": "dc",
  }
  
  def _raise_serialization_error(text):
      raise TypeError(
          "cannot serialize %r (type %s)" % (text, type(text).__name__)
          )
  
  def _encode(text, encoding):
      try:
          return text.encode(encoding, "xmlcharrefreplace")
      except (TypeError, AttributeError):
          _raise_serialization_error(text)
  
  def _escape_cdata(text, encoding):
      # escape character data
      try:
          # it's worth avoiding do-nothing calls for strings that are
          # shorter than 500 character, or so.  assume that's, by far,
          # the most common case in most applications.
          if "&" in text:
              text = text.replace("&", "&amp;")
          if "<" in text:
              text = text.replace("<", "&lt;")
          if ">" in text:
              text = text.replace(">", "&gt;")
          return text.encode(encoding, "xmlcharrefreplace")
      except (TypeError, AttributeError):
          _raise_serialization_error(text)
  
  def _escape_attrib(text, encoding):
      # escape attribute value
      try:
          if "&" in text:
              text = text.replace("&", "&amp;")
          if "<" in text:
              text = text.replace("<", "&lt;")
          if ">" in text:
              text = text.replace(">", "&gt;")
          if "\"" in text:
              text = text.replace("\"", "&quot;")
          if "\n" in text:
              text = text.replace("\n", "&#10;")
          return text.encode(encoding, "xmlcharrefreplace")
      except (TypeError, AttributeError):
          _raise_serialization_error(text)
  
  def _escape_attrib_html(text, encoding):
      # escape attribute value
      try:
          if "&" in text:
              text = text.replace("&", "&amp;")
          if ">" in text:
              text = text.replace(">", "&gt;")
          if "\"" in text:
              text = text.replace("\"", "&quot;")
          return text.encode(encoding, "xmlcharrefreplace")
      except (TypeError, AttributeError):
          _raise_serialization_error(text)
  
  # --------------------------------------------------------------------
  
  ##
  # Generates a string representation of an XML element, including all
  # subelements.
  #
  # @param element An Element instance.
  # @keyparam encoding Optional output encoding (default is US-ASCII).
  # @keyparam method Optional output method ("xml", "html", "text" or
  #     "c14n"; default is "xml").
  # @return An encoded string containing the XML data.
  # @defreturn string
  
  def tostring(element, encoding=None, method=None):
      class dummy:
          pass
      data = []
      file = dummy()
      file.write = data.append
      ElementTree(element).write(file, encoding, method=method)
      return "".join(data)
  
  ##
  # Generates a string representation of an XML element, including all
  # subelements.  The string is returned as a sequence of string fragments.
  #
  # @param element An Element instance.
  # @keyparam encoding Optional output encoding (default is US-ASCII).
  # @keyparam method Optional output method ("xml", "html", "text" or
  #     "c14n"; default is "xml").
  # @return A sequence object containing the XML data.
  # @defreturn sequence
  # @since 1.3
  
  def tostringlist(element, encoding=None, method=None):
      class dummy:
          pass
      data = []
      file = dummy()
      file.write = data.append
      ElementTree(element).write(file, encoding, method=method)
      # FIXME: merge small fragments into larger parts
      return data
  
  ##
  # Writes an element tree or element structure to sys.stdout.  This
  # function should be used for debugging only.
  # <p>
  # The exact output format is implementation dependent.  In this
  # version, it's written as an ordinary XML file.
  #
  # @param elem An element tree or an individual element.
  
  def dump(elem):
      # debugging
      if not isinstance(elem, ElementTree):
          elem = ElementTree(elem)
      elem.write(sys.stdout)
      tail = elem.getroot().tail
      if not tail or tail[-1] != "\n":
          sys.stdout.write("\n")
  
  # --------------------------------------------------------------------
  # parsing
  
  ##
  # Parses an XML document into an element tree.
  #
  # @param source A filename or file object containing XML data.
  # @param parser An optional parser instance.  If not given, the
  #     standard {@link XMLParser} parser is used.
  # @return An ElementTree instance
  
  def parse(source, parser=None):
      tree = ElementTree()
      tree.parse(source, parser)
      return tree
  
  ##
  # Parses an XML document into an element tree incrementally, and reports
  # what's going on to the user.
  #
  # @param source A filename or file object containing XML data.
  # @param events A list of events to report back.  If omitted, only "end"
  #     events are reported.
  # @param parser An optional parser instance.  If not given, the
  #     standard {@link XMLParser} parser is used.
  # @return A (event, elem) iterator.
  
  def iterparse(source, events=None, parser=None):
      close_source = False
      if not hasattr(source, "read"):
          source = open(source, "rb")
          close_source = True
      try:
          if not parser:
              parser = XMLParser(target=TreeBuilder())
          return _IterParseIterator(source, events, parser, close_source)
      except:
          if close_source:
              source.close()
          raise
  
  class _IterParseIterator(object):
  
      def __init__(self, source, events, parser, close_source=False):
          self._file = source
          self._close_file = close_source
          self._events = []
          self._index = 0
          self._error = None
          self.root = self._root = None
          self._parser = parser
          # wire up the parser for event reporting
          parser = self._parser._parser
          append = self._events.append
          if events is None:
              events = ["end"]
          for event in events:
              if event == "start":
                  try:
                      parser.ordered_attributes = 1
                      parser.specified_attributes = 1
                      def handler(tag, attrib_in, event=event, append=append,
                                  start=self._parser._start_list):
                          append((event, start(tag, attrib_in)))
                      parser.StartElementHandler = handler
                  except AttributeError:
                      def handler(tag, attrib_in, event=event, append=append,
                                  start=self._parser._start):
                          append((event, start(tag, attrib_in)))
                      parser.StartElementHandler = handler
              elif event == "end":
                  def handler(tag, event=event, append=append,
                              end=self._parser._end):
                      append((event, end(tag)))
                  parser.EndElementHandler = handler
              elif event == "start-ns":
                  def handler(prefix, uri, event=event, append=append):
                      try:
                          uri = (uri or "").encode("ascii")
                      except UnicodeError:
                          pass
                      append((event, (prefix or "", uri or "")))
                  parser.StartNamespaceDeclHandler = handler
              elif event == "end-ns":
                  def handler(prefix, event=event, append=append):
                      append((event, None))
                  parser.EndNamespaceDeclHandler = handler
              else:
                  raise ValueError("unknown event %r" % event)
  
      def next(self):
          try:
              while 1:
                  try:
                      item = self._events[self._index]
                      self._index += 1
                      return item
                  except IndexError:
                      pass
                  if self._error:
                      e = self._error
                      self._error = None
                      raise e
                  if self._parser is None:
                      self.root = self._root
                      break
                  # load event buffer
                  del self._events[:]
                  self._index = 0
                  data = self._file.read(16384)
                  if data:
                      try:
                          self._parser.feed(data)
                      except SyntaxError as exc:
                          self._error = exc
                  else:
                      self._root = self._parser.close()
                      self._parser = None
          except:
              if self._close_file:
                  self._file.close()
              raise
          if self._close_file:
              self._file.close()
          raise StopIteration
  
      def __iter__(self):
          return self
  
  ##
  # Parses an XML document from a string constant.  This function can
  # be used to embed "XML literals" in Python code.
  #
  # @param source A string containing XML data.
  # @param parser An optional parser instance.  If not given, the
  #     standard {@link XMLParser} parser is used.
  # @return An Element instance.
  # @defreturn Element
  
  def XML(text, parser=None):
      if not parser:
          parser = XMLParser(target=TreeBuilder())
      parser.feed(text)
      return parser.close()
  
  ##
  # Parses an XML document from a string constant, and also returns
  # a dictionary which maps from element id:s to elements.
  #
  # @param source A string containing XML data.
  # @param parser An optional parser instance.  If not given, the
  #     standard {@link XMLParser} parser is used.
  # @return A tuple containing an Element instance and a dictionary.
  # @defreturn (Element, dictionary)
  
  def XMLID(text, parser=None):
      if not parser:
          parser = XMLParser(target=TreeBuilder())
      parser.feed(text)
      tree = parser.close()
      ids = {}
      for elem in tree.iter():
          id = elem.get("id")
          if id:
              ids[id] = elem
      return tree, ids
  
  ##
  # Parses an XML document from a string constant.  Same as {@link #XML}.
  #
  # @def fromstring(text)
  # @param source A string containing XML data.
  # @return An Element instance.
  # @defreturn Element
  
  fromstring = XML
  
  ##
  # Parses an XML document from a sequence of string fragments.
  #
  # @param sequence A list or other sequence containing XML data fragments.
  # @param parser An optional parser instance.  If not given, the
  #     standard {@link XMLParser} parser is used.
  # @return An Element instance.
  # @defreturn Element
  # @since 1.3
  
  def fromstringlist(sequence, parser=None):
      if not parser:
          parser = XMLParser(target=TreeBuilder())
      for text in sequence:
          parser.feed(text)
      return parser.close()
  
  # --------------------------------------------------------------------
  
  ##
  # Generic element structure builder.  This builder converts a sequence
  # of {@link #TreeBuilder.start}, {@link #TreeBuilder.data}, and {@link
  # #TreeBuilder.end} method calls to a well-formed element structure.
  # <p>
  # You can use this class to build an element structure using a custom XML
  # parser, or a parser for some other XML-like format.
  #
  # @param element_factory Optional element factory.  This factory
  #    is called to create new Element instances, as necessary.
  
  class TreeBuilder(object):
  
      def __init__(self, element_factory=None):
          self._data = [] # data collector
          self._elem = [] # element stack
          self._last = None # last element
          self._tail = None # true if we're after an end tag
          if element_factory is None:
              element_factory = Element
          self._factory = element_factory
  
      ##
      # Flushes the builder buffers, and returns the toplevel document
      # element.
      #
      # @return An Element instance.
      # @defreturn Element
  
      def close(self):
          assert len(self._elem) == 0, "missing end tags"
          assert self._last is not None, "missing toplevel element"
          return self._last
  
      def _flush(self):
          if self._data:
              if self._last is not None:
                  text = "".join(self._data)
                  if self._tail:
                      assert self._last.tail is None, "internal error (tail)"
                      self._last.tail = text
                  else:
                      assert self._last.text is None, "internal error (text)"
                      self._last.text = text
              self._data = []
  
      ##
      # Adds text to the current element.
      #
      # @param data A string.  This should be either an 8-bit string
      #    containing ASCII text, or a Unicode string.
  
      def data(self, data):
          self._data.append(data)
  
      ##
      # Opens a new element.
      #
      # @param tag The element name.
      # @param attrib A dictionary containing element attributes.
      # @return The opened element.
      # @defreturn Element
  
      def start(self, tag, attrs):
          self._flush()
          self._last = elem = self._factory(tag, attrs)
          if self._elem:
              self._elem[-1].append(elem)
          self._elem.append(elem)
          self._tail = 0
          return elem
  
      ##
      # Closes the current element.
      #
      # @param tag The element name.
      # @return The closed element.
      # @defreturn Element
  
      def end(self, tag):
          self._flush()
          self._last = self._elem.pop()
          assert self._last.tag == tag,\
                 "end tag mismatch (expected %s, got %s)" % (
                     self._last.tag, tag)
          self._tail = 1
          return self._last
  
  ##
  # Element structure builder for XML source data, based on the
  # <b>expat</b> parser.
  #
  # @keyparam target Target object.  If omitted, the builder uses an
  #     instance of the standard {@link #TreeBuilder} class.
  # @keyparam html Predefine HTML entities.  This flag is not supported
  #     by the current implementation.
  # @keyparam encoding Optional encoding.  If given, the value overrides
  #     the encoding specified in the XML file.
  # @see #ElementTree
  # @see #TreeBuilder
  
  class XMLParser(object):
  
      def __init__(self, html=0, target=None, encoding=None):
          try:
              from xml.parsers import expat
          except ImportError:
              try:
                  import pyexpat as expat
              except ImportError:
                  raise ImportError(
                      "No module named expat; use SimpleXMLTreeBuilder instead"
                      )
          parser = expat.ParserCreate(encoding, "}")
          if target is None:
              target = TreeBuilder()
          # underscored names are provided for compatibility only
          self.parser = self._parser = parser
          self.target = self._target = target
          self._error = expat.error
          self._names = {} # name memo cache
          # callbacks
          parser.DefaultHandlerExpand = self._default
          parser.StartElementHandler = self._start
          parser.EndElementHandler = self._end
          parser.CharacterDataHandler = self._data
          # optional callbacks
          parser.CommentHandler = self._comment
          parser.ProcessingInstructionHandler = self._pi
          # let expat do the buffering, if supported
          try:
              self._parser.buffer_text = 1
          except AttributeError:
              pass
          # use new-style attribute handling, if supported
          try:
              self._parser.ordered_attributes = 1
              self._parser.specified_attributes = 1
              parser.StartElementHandler = self._start_list
          except AttributeError:
              pass
          self._doctype = None
          self.entity = {}
          try:
              self.version = "Expat %d.%d.%d" % expat.version_info
          except AttributeError:
              pass # unknown
  
      def _raiseerror(self, value):
          err = ParseError(value)
          err.code = value.code
          err.position = value.lineno, value.offset
          raise err
  
      def _fixtext(self, text):
          # convert text string to ascii, if possible
          try:
              return text.encode("ascii")
          except UnicodeError:
              return text
  
      def _fixname(self, key):
          # expand qname, and convert name string to ascii, if possible
          try:
              name = self._names[key]
          except KeyError:
              name = key
              if "}" in name:
                  name = "{" + name
              self._names[key] = name = self._fixtext(name)
          return name
  
      def _start(self, tag, attrib_in):
          fixname = self._fixname
          fixtext = self._fixtext
          tag = fixname(tag)
          attrib = {}
          for key, value in attrib_in.items():
              attrib[fixname(key)] = fixtext(value)
          return self.target.start(tag, attrib)
  
      def _start_list(self, tag, attrib_in):
          fixname = self._fixname
          fixtext = self._fixtext
          tag = fixname(tag)
          attrib = {}
          if attrib_in:
              for i in range(0, len(attrib_in), 2):
                  attrib[fixname(attrib_in[i])] = fixtext(attrib_in[i+1])
          return self.target.start(tag, attrib)
  
      def _data(self, text):
          return self.target.data(self._fixtext(text))
  
      def _end(self, tag):
          return self.target.end(self._fixname(tag))
  
      def _comment(self, data):
          try:
              comment = self.target.comment
          except AttributeError:
              pass
          else:
              return comment(self._fixtext(data))
  
      def _pi(self, target, data):
          try:
              pi = self.target.pi
          except AttributeError:
              pass
          else:
              return pi(self._fixtext(target), self._fixtext(data))
  
      def _default(self, text):
          prefix = text[:1]
          if prefix == "&":
              # deal with undefined entities
              try:
                  self.target.data(self.entity[text[1:-1]])
              except KeyError:
                  from xml.parsers import expat
                  err = expat.error(
                      "undefined entity %s: line %d, column %d" %
                      (text, self._parser.ErrorLineNumber,
                      self._parser.ErrorColumnNumber)
                      )
                  err.code = 11 # XML_ERROR_UNDEFINED_ENTITY
                  err.lineno = self._parser.ErrorLineNumber
                  err.offset = self._parser.ErrorColumnNumber
                  raise err
          elif prefix == "<" and text[:9] == "<!DOCTYPE":
              self._doctype = [] # inside a doctype declaration
          elif self._doctype is not None:
              # parse doctype contents
              if prefix == ">":
                  self._doctype = None
                  return
              text = text.strip()
              if not text:
                  return
              self._doctype.append(text)
              n = len(self._doctype)
              if n > 2:
                  type = self._doctype[1]
                  if type == "PUBLIC" and n == 4:
                      name, type, pubid, system = self._doctype
                  elif type == "SYSTEM" and n == 3:
                      name, type, system = self._doctype
                      pubid = None
                  else:
                      return
                  if pubid:
                      pubid = pubid[1:-1]
                  if hasattr(self.target, "doctype"):
                      self.target.doctype(name, pubid, system[1:-1])
                  elif self.doctype is not self._XMLParser__doctype:
                      # warn about deprecated call
                      self._XMLParser__doctype(name, pubid, system[1:-1])
                      self.doctype(name, pubid, system[1:-1])
                  self._doctype = None
  
      ##
      # (Deprecated) Handles a doctype declaration.
      #
      # @param name Doctype name.
      # @param pubid Public identifier.
      # @param system System identifier.
  
      def doctype(self, name, pubid, system):
          """This method of XMLParser is deprecated."""
          warnings.warn(
              "This method of XMLParser is deprecated.  Define doctype() "
              "method on the TreeBuilder target.",
              DeprecationWarning,
              )
  
      # sentinel, if doctype is redefined in a subclass
      __doctype = doctype
  
      ##
      # Feeds data to the parser.
      #
      # @param data Encoded data.
  
      def feed(self, data):
          try:
              self._parser.Parse(data, 0)
          except self._error, v:
              self._raiseerror(v)
  
      ##
      # Finishes feeding data to the parser.
      #
      # @return An element structure.
      # @defreturn Element
  
      def close(self):
          try:
              self._parser.Parse("", 1) # end of data
          except self._error, v:
              self._raiseerror(v)
          tree = self.target.close()
          del self.target, self._parser # get rid of circular references
          return tree
  
  # compatibility
  XMLTreeBuilder = XMLParser
  
  # workaround circular import.
  try:
      from ElementC14N import _serialize_c14n
      _serialize["c14n"] = _serialize_c14n
  except ImportError:
      pass
  