Stack data structure in python

Question

I have 2 issues with the code below:

1. push(o) throws an exception TypeError: can only assign an iterable.

2. Should I throw an exception if pop() is invoked on an empty stack ?

   class Stack(object):      def __init__(self):         self.storage = []      def isEmpty(self):         return len(self.storage) == 0      def push(self,p):         self.storage[:0] = p      def pop(self):         """issue: throw exception?"""         return None 

Answer 1

No need to jump through these loops, See 5.1.1 Using Lists as Stacks

If you insist on having methods isEmpty() and push() you can do:

class stack(list):     def push(self, item):         self.append(item)     def isEmpty(self):         return not self 

Answer 2

You are right to use composition instead of inheritance, because inheritance brings methods in that you don't want to expose.

class Stack:   def __init__(self):     self.__storage = []    def isEmpty(self):     return len(self.__storage) == 0    def push(self,p):     self.__storage.append(p)    def pop(self):     return self.__storage.pop() 

This way your interface works pretty much like list (same behavior on pop for example), except that you've locked it to ensure nobody messes with the internals.