Queue operations in Python

A queue has two main operations:

• ENQUEUE: insert an element at the REAR. Inserting into a full queue causes overflow.
• DEQUEUE: remove the element at the FRONT. Removing from an empty queue causes underflow.

Supporting operations:

• IS EMPTY: check whether the queue is empty, to avoid underflow.
• PEEK: look at the front element without removing it.
• IS FULL: check whether the queue is full, to avoid overflow.

In Python, a list works as a queue, with the left end as the FRONT and the right end as the REAR:

• myQueue = list() creates an empty queue.
• enqueue uses append(element), adding at the rear.
• dequeue uses pop(0), removing the element at index 0, the front.
• size() uses len().
• peek() returns myQueue[0], the front element.

IS FULL is not needed in Python, because a list has no fixed size: it simply grows as elements are added.

For example, with the queue [P1, P2]: dequeue removes P1 from the front, leaving [P2]; then enqueue P3 adds it at the rear, giving [P2, P3].