check if a string is parentheses balanced

validate_parentheses

def is_parentheses_balanced(expression):

    stack = []

    for symbol in expression:

        if symbol == '(':
            stack.append(symbol)

        if symbol == ')':
            if (not stack) or stack.pop(-1) != '(':
                return False

    if stack:
        return False

    return True

print is_parentheses_balanced('((())())()')