'Parse a (non-nested) parenthesised list from the line'

def arg_plist(self, line):

    if (not line):
        raise IllegalClientResponse('Missing    argument')
    if (line[0] != '('):
        raise IllegalClientResponse('Missing    parenthesis')
    i = line.find(')')
    if (i == (-1)):
        raise IllegalClientResponse('Mismatched    parenthesis')
    return (parseNestedParens(line[1:i], 0), line[(i + 2):])
