Complete the is_empty method for a stack implemented using a Python list. class Stack:     def __init__(self):         self._items = []     def push(self, item):         self._items.append(item)     def pop(self):         if not self.is_empty():             return self._items.pop()         else:             raise IndexError("Stack is empty")     def is_empty(self):         _________ # Line to complete