def __init__(self, field_instance, sequence):
        """Constructor.

        Args:
          field_instance: Instance of field that validates the list.
          sequence: List or tuple to construct list from.
        """
        if not field_instance.repeated:
            raise FieldDefinitionError(
                'FieldList may only accept repeated fields')
        self.__field = field_instance
        self.__field.validate(sequence)
        list.__init__(self, sequence)