week #2 ----Stacks

In the second week, I learn Stacks ADT, which include the following operations:

• __init__ (Initialize a new empty stack)
• push (add a new item to the stack
• pop (remove and return an item from the stack. the item that is returned is always the last one that was added)
• is_empty (check whether the stack is empty)

The data structure is LIFO called "Last in, First out"