parentheses_match.py

MAPPING = {
	'{': '}',
	'(': ')',
	'[': ']',
}

def is_open(c):
	return c in MAPPING


def is_close(c):
	return c in MAPPING.values()


def is_matched(c1, c2):
	return MAPPING.get(c1) == c2


def func(s, c):
	if not s:
		return c

	if is_open(c):
		return s + c

	if is_close(c) and is_matched(s[-1], c):
		return s[:-1]

	raise ValueError()


def is_matched(s):
	try:
		return not bool(reduce(func, s, ''))
	except ValueError:
		return False


if __name__ == '__main__':
	valids = (
		'',
		'()',
		'[]',
		'{}',
		'([]{})',
		'([]{()})',
	)
	invalids = (
		'(',
		']',
		'(()',
		'([)',
		'())',
		'()]',
		'({}]',
	)
	for s in valids:
		print s, is_matched(s)
	for s in invalids:
		print s, is_matched(s)