test.py

#!/usr/bin/env python

stack = []
matches = {
        # open -> close
        '(': ')',
        '{': '}',
        '[': ']',
        }
open_chars = matches.keys()
close_chars = matches.values()

def check_string(s):
    stack = []
    for c in s:
        if c in open_chars:
            # push what it should match
            stack.append(matches[c])
        elif c in close_chars:
            try:
                should_match = stack.pop()
            except IndexError:
                # unbalanced
                return "NO"
            if c != should_match:
                # bad match, we're done
                return "NO"
    if len(stack) == 0:
        return "YES"
    else:
        # unbalanced
        return "NO"

samples = [ "{}[]()", "{[}]" ]
samples = [
    "[{()()}({[]})]({}[({})])((((((()[])){}))[]{{{({({({{{{{{}}}}}})})})}}}))[][][]{",
    "[{()()}({[]})]({}[({})])((((((()[])){}))[]{{{({({({{{{{{}}}}}})})})}}}))[][][]]",
    "[{()([)}({[]})]({}[({})])((((((()[])){}))[]{{{({({({{{{{{}}}}}})})})}}}))[][][]",
    "{}[]()",
    "{[}]"
] 

answers = []
for s in samples:
    answers.append(check_string(s))
print repr(answers)