[Tutor] Stack problem usind Python2.6

[James Reynolds]

On Thu, Jul 21, 2011 at 5:16 PM, David Merrick <merrickdav at gmail.com> wrote:

> ##from stack import Stack
>
> class Stack:
>     def __init__(self):
>         self.items =[]
>
>     def isEmpty(self):
>         return self.items ==[]
>
>     def push(self,item):
>         self.items.append(item)
>
>     def pop(self,item):
>         self.items.pop()
>
>     def peek(self):
>         return  self.items[len(self.items)-1]
>
>     def size(self):
>         return len(self.items)
>
> 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+=1
>         if balanced and  s.isEmpty():
>             return True
>         else:
>             return False
>
> def matches(open,close):
>     opens = "([{"
>     closers = ")]}"
>
>     opens.index(open) == closers.index(close)
>
> symbolString = "()"
> print(parChecker(symbolString))
>
> *Output*
>
> () returns False should be true
> (() returns False which is correct
>
> I can't find the error please help me
>
> --
> Dave Merrick
>
> merrickdav at gmail.com
>
> Ph   03 3423 121
> Cell 027 3089 169
>
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> To unsubscribe or change subscription options:
> http://mail.python.org/mailman/listinfo/tutor
>
>




A couple more points:

* I did just run it with the break statements where you have 'balanced =
False'
* the method Stack needs a return statement (otherwise, it will return
None), as all functions without a return statement do.
* you should either get rid of the argument for pop in Stack or make it an
optional argument (item = None) if you intended to do something with item.
* You of course need to tab in this block if you decide to go the 'break'
route:

    if s.isEmpty():
        return True
    else:
        return False
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/tutor/attachments/20110721/4bb11230/attachment.html>