def __field_to_parameter_type(self, field):
<EOL>variant = field.variant<EOL>if variant == messages.Variant.MESSAGE:<EOL><INDENT>raise TypeError('<STR_LIT>')<EOL><DEDENT>custom_variant_map = {<EOL>messages.Variant.SINT32: '<STR_LIT>',<EOL>messages.Variant.SINT64: '<STR_LIT>',<EOL>messages.Variant.BOOL: '<STR_LIT>',<EOL>messages.Variant.ENUM: '<STR_LIT:string>',<EOL>}<EOL>return custom_variant_map.get(variant) or variant.name.lower()<EOL>
Converts the field variant type into a string describing the parameter.

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

        Returns:
          A string corresponding to the variant enum of the field, with a few
            exceptions. In the case of signed ints, the 's' is dropped; for the BOOL
            variant, 'boolean' is used; and for the ENUM variant, 'string' is used.

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