PYTHON
Implement a LIFO Stack Using Python Lists
Understand how to implement a Last-In, First-Out (LIFO) stack data structure in Python using simple list operations like append and pop, essential for many algorithms.
class Stack:
def __init__(self):
self._items = []
def is_empty(self):
return not bool(self._items)
def push(self, item):
self._items.append(item) # Add to the end of the list
def pop(self):
if self.is_empty():
raise IndexError("pop from empty stack")
return self._items.pop() # Remove from the end of the list
def peek(self):
if self.is_empty():
raise IndexError("peek from empty stack")
return self._items[-1]
def size(self):
return len(self._items)
# Example Usage:
my_stack = Stack()
my_stack.push(10)
my_stack.push(20)
print(f"Stack size: {my_stack.size()}") # Output: 2
print(f"Top element: {my_stack.peek()}") # Output: 20
print(f"Popped: {my_stack.pop()}") # Output: 20
print(f"Stack size after pop: {my_stack.size()}") # Output: 1
my_stack.push(30)
print(f"Popped: {my_stack.pop()}") # Output: 30
print(f"Is stack empty? {my_stack.is_empty()}") # Output: False
print(f"Popped: {my_stack.pop()}") # Output: 10
print(f"Is stack empty? {my_stack.is_empty()}") # Output: True
How it works: This snippet demonstrates implementing a Last-In, First-Out (LIFO) stack using a standard Python list. The `push` operation uses `append()` to add elements to the end of the list, and `pop` uses the list's `pop()` method (without an index) to remove and return the last element added. This natural behavior of Python lists makes them suitable for efficient stack implementations, as adding/removing from the end of a list is an O(1) operation.