code: def _read_marcxml(xml):
      
      # read file, if `xml` is valid file path
      marc_xml = _read_content_or_path(xml)
  
  
      # process input file - convert it from possible OAI to MARC XML and add
      # required XML namespaces
      marc_xml = _oai_to_xml(marc_xml)
      marc_xml = _add_namespace(marc_xml)
  
      file_obj = StringIO.StringIO(marc_xml)
  
      return ET.parse(file_obj)
docs: Read MARC XML or OAI file, convert, add namespace and return XML in
      required format with all necessities.
  
      Args:
          xml (str): Filename or XML string. Don't use ``\\n`` in case of
                     filename.
  
      Returns:
          obj: Required XML parsed with ``lxml.etree``.