code: def _make_seq_field_type(checked_class, item_type):
      
      type_ = _seq_field_types.get((checked_class, item_type))
      if type_ is not None:
          return type_
  
      class TheType(checked_class):
          __type__ = item_type
  
          def __reduce__(self):
              return (_restore_seq_field_pickle,
                      (checked_class, item_type, list(self)))
  
      suffix = SEQ_FIELD_TYPE_SUFFIXES[checked_class]
      TheType.__name__ = _types_to_names(TheType._checked_types) + suffix
      _seq_field_types[checked_class, item_type] = TheType
      return TheType
docs: Create a subclass of the given checked class with the given item type.