class Stack:

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

    def __init__(self):
        """ (Stack) -> Nonetype

        Initialize new Stack self.

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

    # this stack is implemented to push and pop at _data[0]!!!
        
    def pop(self):
        """ (Stack) -> object

        Remove and return the top item from self.

        >>> s = Stack()
        >>> s.push(2)
        >>> s.push(3)
        >>> s.pop()
        3
        """
        return self._data.pop(0)
    
    def is_empty(self):
        """ (Stack) -> bool

        Return whether the self is empty.

        >>> s = Stack()
        >>> s.push(4)
        >>> s.pop()
        4
        >>> s.is_empty()
        True
        """
        return len(self._data) == 0
    
    def push(self, o):
        """ (Stack, object) -> NoneType

        Place object o on top of Stack self.
        """
        self._data.insert(0,o)
        
        # implementation of __eq__, __str__,
        # and __repr__ left as an exercise

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")