"""
This implementation of the Stack ADT comes from 
   Problem Solving with Algorithms and Data Structures using Python
   3rd Edition
   Miller, Ranum, and Yasinovskyy

It is constructed utilizing the built in Python list and adding things to the "right" or "bottom" end of the list.
"""

class Stack:
    """Stack implementation as a list"""

    def __init__(self):
        """Create new stack"""
        self._items = []

    def is_empty(self):
        """Check if the stack is empty"""
        return not bool(self._items)

    def push(self, item):
        """Add an item to the stack"""
        self._items.append(item)

    def pop(self):
        """Remove an item from the stack"""
        return self._items.pop()

    def peek(self):
        """Get the value of the top item in the stack"""
        return self._items[-1]

    def size(self):
        """Get the number of items in the stack"""
        return len(self._items)