"""
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."""

        self._data = []

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

        return self._data.pop()

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

        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 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")