stack.py

class Stack:
    def __init__(self):
        self.items = []

    def is_empty(self):
        return len(self.items) == 0

    def push(self, item):
        self.items.append(item)

    def pop(self):
        return self.items.pop()

    def peek(self):
        if self.items:
            return self.items[-1]
        return None

    def __len__(self):
        # in python the `len` function is preferred to `size` methods
        return len(self.items)

    def __bool__(self):
        # lets us use the stack as a conditional
        return bool(self.items)
    
s = Stack()
print(s.is_empty())
s.push(1)
s.push('two')
s.is_empty()
s.size()
s.pop()
s.pop()
s.is_empty()