"""Stack ADT.

Operations:
	pop: remove and return top item
        push(item): store item on top of stack
        is_empty: return whether stack is empty.
"""

class Stack:

    """A last-in, first-out (LIFO) stack of items"""

    def __init__(self: 'Stack') -> None:
        """A new empty Stack.

        >>> isinstance(Stack(), Stack)
        True
        """
        self._data = []

    def pop(self: 'Stack') -> object:
        """Remove and return the top item.

        >>> s = Stack()
        >>> s.push(2)
        >>> s.push(3)
        >>> s.pop()
        3
        """
        return self._data.pop()

    def is_empty(self: 'Stack') -> bool:
        """Return whether the stack is empty.

        >>> s = Stack()
        >>> s.push(4)
        >>> s.pop()
        4
        >>> s.is_empty()
        True
        """
        return self._data == []

    def push(self: 'Stack', o: object) -> None:
        """Place o on top of the stack."""
        self._data.append(o)

if __name__  ==  '__main__':
    import doctest
    doctest.testmod()
    import time
    s = Stack()
    items = range(100000)

    # start the clock
    start = time.time()

    for i in items:
        s.push(i)

    for i in items:
        s.pop()

    end = time.time()
    print ("It took ", end - start, "to push/pop", len(items), "items")