Create a file lab3.py and import your Stack class to implement the following exercise. Test your implementation of this exercise

Listing 3.4 (Validation of General Parentheses-expressions)

from pythonds.basic import Stack def parChecker(symbolString): s = Stack()

balanced = True index = 0

while index < len(symbolString) and balanced: symbol = symbolString[index] if symbol in "([{": s.push(symbol) else: if s.isEmpty(): balanced = False else: top = s.pop() if not matches(top, symbol): balanced = False

index = index + 1

if balanced and s.isEmpty(): return True else: return False

def matches(open, close): opens = "([{" closers = ")]}"

return opens.index(open) == closers.index(close)