Python Data Structures and Algorithms

Bracket-matching application

Now let us look at an example of how we can use our stack implementation. We are going to write a little function that will verify whether a statement containing brackets--(, [, or {--is balanced, that is, whether the number of closing brackets matches the number of opening brackets. It will also ensure that one pair of brackets really is contained in another:

    def check_brackets(statement):         stack = Stack()         for ch in statement:             if ch in ('{', '[', '('):                 stack.push(ch)             if ch in ('}', ']', ')'):                 last = stack.pop()             if last is '{' and ch is '}':                 continue             elif last is '[' and ch is ']':                 continue             elif last is '(' and ch is ')':                 continue             else:                 return False     if stack.size > 0:         return False     else:  return ...