Well formed

well-formed.py

from sys import argv

def is_left(a):
    if a == '[' or a == '(' or a == '{': return True
    return False

def is_right(a):
    if a == ']' or a == '}' or a == ')': return True
    return False

def is_match(left, right):
    if left == '(' and right == ')': return True
    if left == '{' and right == '}': return True
    if left == '[' and right == ']': return True
    return False

for string in open(argv[1], 'r'):
    string = string.rstrip()
    l = len(string)

    if l % 2 != 0:
        print 'False'
        continue

    is_formed = True
    stack = []
    for char in string:
        if is_right(char):
            if len(stack) < 1:
                is_formed = False
                break

            open_char = stack.pop()
            if not is_match(open_char, char):
                is_formed = False
                break
        else:
            # left char
            stack.append(char)

    print str(is_formed)