code: def __meta_metadata(self, field, key):
          
          mf = ''
          try:
              mf = str([f[key] for f in self.metadata
                       if f['field_name'] == field][0])
          except IndexError:
              print("%s not in metadata field:%s" % (key, field))
              return mf
          else:
              return mf
docs: Return the value for key for the field in the metadata