Define a class Queue which implements the abstract data type queue. As part of your definition of Queue, define the following methods:

• __init__(self) which creates an empty queue.
• enqueue(self, x) which adds x to the end of the queue.
• dequeue(self) which removes and returns the first (= oldest) element in the queue.
• __len__(self) which returns the total number of elements currently in the queue.

You are free to define and use suitable instance variables to store the items in the queue. If the method dequeue is called for an empty queue, it should execute the statement

 raise IndexError