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

    def istEmpty(self):
        return not bool(self.items)

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

    def pop(self):
        value = self.items.pop()
        if value is not None:
            return value
        else:
            print('Stack is Empty.')

    def size(self):
        return len(self.items)

    def peek(self):
        if self.items:
            return self.items[-1]
        else:
            print('Stack is Empty.')

    def __repr__(self):
        return repr(self.items)

    if __name__ == "__main__":
        stack = Stack()
        print('Is Stack Empty? {0}'.format(stack.isEmpty()))
        print('Add 0-9 number to the stack.')
        for i in range(10):
            stack.push(i)
        print('Stack Size: {0}'.format(stack.size()))
        print('peek: {0}'.format(stack.peek()))
        print('pop: {0}'.format(stack.pop()))
        print('peek: {0}'.format(stack.peek()))
        print('Is Stack Empty? {0}'.format(stack.isEmpty()))
        print(stack)

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

    def istEmpty(self):
        return not bool(self.items)

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

    def pop(self):
        value = self.items.pop()
        if value is not None:
            return value
        else:
            print('Stack is Empty.')

    def size(self):
        return len(self.items)

    def peek(self):
        if self.items:
            return self.items[-1]
        else:
            print('Stack is Empty.')

    def __repr__(self):
        return repr(self.items)

    if __name__ == "__main__":
        stack = Stack()
        print('Is Stack Empty? {0}'.format(stack.isEmpty()))
        print('Add 0-9 number to the stack.')
        for i in range(10):
            stack.push(i)
        print('Stack Size: {0}'.format(stack.size()))
        print('peek: {0}'.format(stack.peek()))
        print('pop: {0}'.format(stack.pop()))
        print('peek: {0}'.format(stack.peek()))
        print('Is Stack Empty? {0}'.format(stack.isEmpty()))
        print(stack)
