Infix to prefix parser and evaluator I wrote in like 10 minutes (meaning don't judge me)

prefix_parser.py

import sys

# Note ('s are not currently supported.  Given we treat them as
# 'frames' they are implicitly simple to recursivly implement.
ops = ['^', '*', '/', '+', '-']

# 1 + 2 -> + 1 2
# 1 + 2 * 3 -> + * 3 2 1
def parser(tokens):
    stack = []
    op_stack = []

    for op in ops:
        for i, token in enumerate(tokens):
            if op == token:
                stack.append(i)
                if i + 1 not in stack: stack.append(i + 1)
                if i - 1 not in stack: stack.append(i - 1)


    return [tokens[i] for i in stack]

# XXX: Note this only does integer mathematics.
def prefix_eval(tokens):

    result = None
    op = None

    resolve = {
            '^': lambda x,y: x ** y,
            '*': lambda x,y: x * y,
            '/': lambda x,y: x / y,
            '+': lambda x,y: x + y,
            '-': lambda x,y: x - y,
            }

    for token in tokens:
        if token in ops:
            op = token
        elif result is not None:
            result = resolve[op](int(result), int(token))
        else:
            result = int(token)

    return result


if __name__ == '__main__':
    parsed = parser(sys.argv[1].split())
    print parsed
    print prefix_eval(parsed)