Split The Number (CodeEval) in Python 3.x

main.py

# coding=utf-8
import sys
import re

CALC_PATTERN = re.compile("([a-z]+)([+-])[a-z]+")


def main():
    with open(sys.argv[1], "r") as f:
        for line in f:
            digit, pattern = line.rstrip().split()

            lp, o = CALC_PATTERN.match(pattern).groups(())
            l = int(digit[:len(lp)])
            r = int(digit[len(lp):])
            if o == '+':
                print(l + r)
            elif o == '-':
                print(l - r)
            else:
                raise ValueError()


if __name__ == "__main__":
    main()