stacks.py

# Python implementations of stacks - List-based implementation and Deque-based implementation 

class ListBasedStack:
    def __init__(self):
        self.stack = []
    
    def push(self, item):
        self.stack.append(item)
    
    def pop(self):
        if not self.is_empty():
            return self.stack.pop()
        raise IndexError("pop from empty stack")
    
    def peek(self):
        if not self.is_empty():
            return self.stack[-1]
        raise IndexError("peek from empty stack")
    
    def is_empty(self):
        return len(self.stack) == 0
    

from collections import deque

class DequeBasedStack:
    def __init__(self):
        self.stack = deque()
    
    def push(self, item):
        self.stack.append(item)
    
    def pop(self):
        if not self.is_empty():
            return self.stack.pop()
        raise IndexError("pop from empty stack")
    
    def peek(self):
        if not self.is_empty():
            return self.stack[-1]
        raise IndexError("peek from empty stack")
    
    def is_empty(self):
        return len(self.stack) == 0

# Test cases
stack = ListBasedStack()
stack.push(1)
stack.push(2)
stack.push(3)
assert stack.peek() == 3
assert stack.pop() == 3
assert stack.peek() == 2
assert stack.pop() == 2
assert stack.peek() == 1
assert stack.pop() == 1
assert stack.is_empty() == True

stack = DequeBasedStack()
stack.push(1)
stack.push(2)
stack.push(3)
assert stack.peek() == 3
assert stack.pop() == 3
assert stack.peek() == 2
assert stack.pop() == 2
assert stack.peek() == 1
assert stack.pop() == 1
assert stack.is_empty() == True