Get the text of the XML node. If path is not None, it will get the text of the descendant of
  source indicated by path.

def get_xml_text(source, path=None):
  """Get the text of the XML node. If path is not None, it will get the text of the descendant of
  source indicated by path.
  """
  if path is None:
    return source.text
  else:
    return get_xml_text(get_xml_child(source, path))