def p_field_id(self, p):
        '''field_id : INTCONSTANT ':'
                    | '''
        if len(p) == 3:

            if p[1] == 0:
                # Prevent users from ever using field ID 0. It's reserved for
                # internal use only.
                raise ThriftParserError(
                    'Line %d: Field ID 0 is reserved for internal use.'
                    % p.lineno(1)
                )

            p[0] = p[1]
        else:
            p[0] = None