code: def get_single_child_from_xml(elem, tag):
      
      children = elem.findall(tag)
      if not children:
          return None
      if len(children) > 1:
          logging.warning('Tag "%s" has more than one child tags with name "%s" in input file, '
                          'ignoring all but the first.',
                          elem.tag, tag)
      return children[0]
docs: Get a single child tag from an XML element.
      Similar to "elem.find(tag)", but warns if there are multiple child tags with the given name.