Prefix expressions [ * + 2 3 4 ]

gistfile1.txt

import itertools

def do_calc(expr):
    stack = []
    for t in expr:
        if   t == '+': stack[-2:] = [stack[-1] + stack[-2]]
        elif t == '*': stack[-2:] = [stack[-1] * stack[-2]]
        elif t == '/': stack[-2:] = [stack[-1] / stack[-2]]
        else: stack.append(t)
    return stack[0]


if __name__ == "__main__":
        import sys
        file = open(sys.argv[1], 'r')
        for j in file.read().split('\n'):
                if j:
                        print do_calc(reversed([i if i in '*/+' else int(i) for i in j.split(' ')]))