code: def parse(self, response, metadata_type):
          
          xml = xmltodict.parse(response.text)
          self.analyze_reply_code(xml_response_dict=xml)
          base = xml.get('RETS', {}).get('METADATA', {}).get(metadata_type, {})
  
          if metadata_type == 'METADATA-SYSTEM':
              syst = base.get('System', base.get('SYSTEM'))
              if not syst:
                  raise ParseError("Could not get the System key from a METADATA-SYSTEM request.")
  
              system_obj = {}
              if syst.get('SystemID'):
                  system_obj['system_id'] = str(syst['SystemID'])
              if syst.get('SystemDescription'):
                  system_obj['system_description'] = str(syst['SystemDescription'])
              if syst.get('Comments'):
                  system_obj['comments'] = syst['Comments']
              if base.get('@Version'):
                  system_obj['version'] = base['@Version']
              return [system_obj]
  
          elif metadata_type == 'METADATA-CLASS':
              key = 'class'
          elif metadata_type == 'METADATA-RESOURCE':
              key = 'resource'
          elif metadata_type == 'METADATA-LOOKUP_TYPE':
              key = 'lookuptype'
          elif metadata_type == 'METADATA-OBJECT':
              key = 'object'
          elif metadata_type == 'METADATA-TABLE':
              key = 'field'
          else:
              msg = "Got an unknown metadata type of {0!s}".format(metadata_type)
              raise ParseError(msg)
  
          # Get the version with the right capitalization from the dictionary
          key_cap = None
          for k in base.keys():
              if k.lower() == key:
                  key_cap = k
  
          if not key_cap:
              msg = 'Could not find {0!s} in the response XML'.format(key)
              raise ParseError(msg)
  
          if isinstance(base[key_cap], list):
              return base[key_cap]
          else:
              return [base[key_cap]]
docs: Parses RETS metadata using the STANDARD-XML format
          :param response: requests Response object
          :param metadata_type: string
          :return parsed: list