myStack

class Node:
    def __init__(self, value, next=None):
        self.value = value
        self.next = next


class Stack:
    def __init__(self):
        self.top = None
        self.bottom = None
        self.length = 0
    
    
    def peek(self):
        return self.top.value
    
    
    def push(self, value):
        if self.isEmpty():
            newNode = Node(value)
            self.bottom = newNode
            self.top = newNode
        else:
            newNode = Node(value, self.top)
            self.top = newNode
        self.length+=1
    
    
    def pop(self):
        if self.isEmpty():
            raise Exception("Stack is empty.")
        elif self.top == self.bottom:
            returnVal = self.bottom.value
            self.top = None
            self.bottom = None
        else:
            returnVal = self.top.value
            self.top = self.top.next
        self.length-=1
        return returnVal
    
    def isEmpty(self):
        return (True if self.length == 0 else False)
    
    
print("Hello World!")
myStack = Stack()

print(myStack.isEmpty())
assert(myStack.isEmpty() == True)

myStack.push(5)
myStack.push(8)
assert(myStack.isEmpty() == False)

assert(myStack.peek()==8)
print(myStack.pop())
assert(myStack.peek()==5)
print(myStack.pop())
assert(myStack.isEmpty() == True)

try:
    print(myStack.pop())
except Exception as e:
    print(f"exception: {e}")

print("Goodbye Cruel World")