Question

I want to be able to pair up all parentheses in a string, if they aren’t paired then then they get their index number and False. It seems like it is repeating some values over and over, i.e cl == pop[1]. I have tried to see where the problem is but I can’t see it no matter how hard I try. So I’m asking if anyone help me to locate the error and maybe even improve my code 😉

def check_parentheses(string):
    pending = 0
    brackets = []
    '''Checks if parens are paired, otherwise they are bad.'''
    parenstack = collections.deque()
    for ch in string:
        if ch in lrmap:
            try:
                cl = string.index(ch, pending)
                pending = cl + 1

            except:
                cl = False

        if ch in lparens:
            parenstack.append([ch, cl])
            print parenstack

        elif ch in rparens:
            try:
                pop = parenstack.pop()

                if lrmap[pop[0]] != ch:
                    print 'wrong type of parenthesis popped from stack',\
                    pop[0], ch, pop[1], cl

                    brackets.append([pop[1], False])
                    brackets.append([cl, False])
                else:
                    brackets.append([pop[1], cl])

            except IndexError:
                print 'no opening parenthesis left in stack'
                brackets.append([cl, False])

    # if we are not out of opening parentheses, we have a mismatch
    for p in parenstack:
        brackets.append([p[1],False])
    return brackets

Answer 1

You can adapt my code to a similar question:

def Evaluate(str):
  stack = []
  pushChars, popChars = "<({[", ">)}]"
  for c in str :
    if c in pushChars :
      stack.append(c)
    elif c in popChars :
      if not len(stack) :
        return False
      else :
        stackTop = stack.pop()
        balancingBracket = pushChars[popChars.index(c)]
        if stackTop != balancingBracket :
          return False
    else :
      return False
  return not len(stack)