Python String Calculator

gistfile1.py

import sys;
def add(numbers):
    result=0; sep=","; nums=numbers
    if(numbers.startswith("//")):
        lines = numbers.splitlines()
        pattern=lines[0][2:]
        if(pattern[0]=="[" and pattern[pattern.length-1]=="]"):
            pattern=pattern[1:pattern.length-1]
        sep=pattern; nums=lines[1]
    nums = nums.replace("\n",sep).split(sep)
    for n in nums:
        i=int(n)
        if(i<0):
            raise ValueError("negative not allowed")
        if(i<=1000):
            result+=i
    return result