Queues in Python

• Enqueue: add element to the rear
• Dequeue: remove element from the front
• Front: view first element
• isEmpty: check if queue is empty

Using List (not efficient for dequeue)

queue = []
queue.append(10)
queue.append(20)

queue.pop(0)  # slow for large lists

Using collections.deque (recommended)

from collections import deque

queue = deque()
queue.append(10)      # enqueue
queue.append(20)

print(queue.popleft())  # dequeue -> 10

Enqueue

queue.append(5)

Dequeue

queue.popleft()

Front

front = queue[0]

isEmpty

is_empty = len(queue) == 0

Circular Queue

A queue where the last position connects back to the first to reuse space.

Priority Queue

Elements are removed based on priority, not insertion order.
Python uses heapq.

import heapq
pq = []
heapq.heappush(pq, 3)
heapq.heappush(pq, 1)
heapq.heappop(pq)  # 1

Scheduling

CPU task scheduling uses queues.

Buffering

Data streaming and IO buffering.

BFS (Breadth First Search)

Queues are core to BFS in graphs and trees.

Queues are essential for order-based processing. Learn deque well because it’s the standard queue tool in Python.