code: def get_padding_lengths(self) -> Dict[str, Dict[str, int]]:
          
          lengths = {}
          for field_name, field in self.fields.items():
              lengths[field_name] = field.get_padding_lengths()
          return lengths
docs: Returns a dictionary of padding lengths, keyed by field name.  Each ``Field`` returns a
          mapping from padding keys to actual lengths, and we just key that dictionary by field name.