def __field_to_parameter_type_and_format(self, field):
<EOL>variant = field.variant<EOL>if variant == messages.Variant.MESSAGE:<EOL><INDENT>raise TypeError('<STR_LIT>')<EOL><DEDENT>return CUSTOM_VARIANT_MAP.get(variant) or (variant.name.lower(), None)<EOL>
Converts the field variant type into a tuple describing the parameter.

        Args:
          field: An instance of a subclass of messages.Field.

        Returns:
          A tuple with the type and format of the field, respectively.

        Raises:
          TypeError: if the field variant is a message variant.