Parsing Parentheses

Stacks are often used for parsing. A simple parsing task is to check whether a string of parentheses are matching.

For example, the string ([]) is matching, because the outer and inner brackets form pairs. ()<>) is not matching, because the last \) has no partner. ([)] is also not matching, because pairs must be either entirely inside or outside other pairs.

def checkParenth(str):
    stack = Stack()
    pushChars, popChars = "<({[", ">)}]"
    for c in str:
        if c in pushChars:
            stack.push(c)
        elif c in popChars:
            if stack.isEmpty():
                return False
            else:
                stackTop = stack.pop()
                # Checks to see whether the opening bracket matches the closing one
                balancingBracket = pushChars[popChars.index(c)]
                if stackTop != balancingBracket:
                    return False
        else:
            return False

    return not stack.isEmpty()

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