A stack is a LIFO (Last-In-First-Out) data structure. Elements are pushed onto and popped from the top.
| Operation | Time |
|---|---|
| Push / Pop | O(1) |
| Peek (top) | O(1) |
stack = []
stack.append(10); stack.append(20) # push
stack.pop() # pop — 20
stack[-1] # peek