user2687481 user2687481 - 3 months ago 11
Python Question

Implementing Stack with Python

I am trying to implement a simple stack with Python using arrays. I was wondering if someone could let me know what's wrong with my code.

class myStack:
def __init__(self):
self = []

def isEmpty(self):
return self == []

def push(self, item):
self.append(item)

def pop(self):
return self.pop(0)

def size(self):
return len(self)

s = myStack()
s.push('1')
s.push('2')
print(s.pop())
print s

Answer

I corrected a few problems below. Also, a 'stack', in abstract programming terms, is usually a collection where you add and remove from the top, but the way you implemented it, you're adding to the top and removing from the bottom, which makes it a queue.

class myStack:
     def __init__(self):
         self.container = []  # You don't want to assign [] to self - when you do that, you're just assigning to a new local variable called `self`.  You want your stack to *have* a list, not *be* a list.

     def isEmpty(self):
         return self.size() == 0   # While there's nothing wrong with self.container == [], there is a builtin function for that purpose, so we may as well use it.  And while we're at it, it's often nice to use your own internal functions, so behavior is more consistent.

     def push(self, item):
         self.container.append(item)  # appending to the *container*, not the instance itself.

     def pop(self):
         return self.container.pop()  # pop from the container, this was fixed from the old version which was wrong

     def size(self):
         return len(self.container)  # length of the container

s = myStack()
s.push('1')
s.push('2')
print(s.pop())
print s