Below __init__(), define a method push() for Stack that takes the parameter value. Inside the method:

• Instantiate a Node with value as an argument and assign it to the variable item (because this item is a node, we have easy access to Node’s class methods)
• Set item‘s next node to the stack’s current top_item using the Node method set_next_node()
• Set the stack instance’s top_item equal to the new item, adding it to the top of the stack

Below push(), define a method pop() for Stack. Inside pop():

• Create a variable item_to_remove and set it equal to the stack’s top_item
• If we’re removing our stack’s top_item, we need to set a new top_item! Set the top_item equal to the node after item_to_remove
• Return the value stored in item_to_remove