Queue in Python – Analytics Vidhya

Introduction

Think about you’re standing in entrance of a grocery store ready on your flip to purchase live performance tickets of your favorite artist. All go to the road formation and transfer from the road on the entrance of it. Pc scientists name this orderliness a queue, which follows the First In, First Out (FIFO) coverage. Programmers discover queues as helpful as different Python information constructions and use them to handle duties, course of asynchronous information, and carry out many different capabilities. On this article we are going to focuses on utilizing queues in Python, the overall overview of the queues, and the significance of queues.

Studying Outcomes

• Perceive what a queue is and its significance in programming.
• Be taught other ways to implement queues in Python.
• ExploExplore varied operations you possibly can carry out on queues.
• Uncover sensible functions of queues.
• Acquire insights into superior queue sorts and their use circumstances.

What’s a Queue?

A queue is a linear information construction that follows the First In First Out (FIFO) precept. It operates by inserting information on the rear finish and deleting information from the entrance finish. This course of ensures that the queue removes the primary inserted aspect first, adhering to the FIFO precept.

Operations on Queues

Listed below are the operations which might be sometimes related to a queue.

• Enqueue: This operation provides an merchandise to the top of the queue. If the queue is full, it leads to an overflow situation. The time complexity for this operation is (O(1)).
• Dequeue: This operation removes an merchandise from the entrance of the queue. Objects comply with the FIFO precept and are eliminated in the identical order they had been added. If the queue is empty, it leads to an underflow situation. The time complexity for this operation is (O(1)).
• Peek or Entrance: This operation retrieves the merchandise on the entrance of the queue with out eradicating it. The time complexity for this operation is (O(1)).
• Rear or Again: This operation retrieves the merchandise on the finish of the queue. The time complexity for this operation is (O(1)).
• IsEmpty: Checking if the queue is empty. Time complexity: O(1) – Fixed time operation.
• IsFull: Checking if the queue is full (if applied with a hard and fast measurement). Time complexity: O(1) – Fixed time operation.
• Dimension: Returns the variety of parts within the queue. Time complexity: O(1) – Fixed time operation in most implementations.

Implementing Queues in Python

There are a number of methods to implement queues in Python:

Utilizing Lists

Python lists can be utilized to implement a queue. Nevertheless, utilizing lists for queues just isn’t environment friendly for giant datasets as a result of eradicating parts from the entrance of an inventory is an O(n) operation.

class ListQueue:
    def __init__(self):
        self.queue = []

    def enqueue(self, merchandise):
        self.queue.append(merchandise)
        print(f"Enqueued: merchandise")

    def dequeue(self):
        if self.is_empty():
            elevate IndexError("Dequeue from an empty queue")
        merchandise = self.queue.pop(0)
        print(f"Dequeued: merchandise")
        return merchandise

    def peek(self):
        if self.is_empty():
            elevate IndexError("Peek from an empty queue")
        print(f"Peek: self.queue[0]")
        return self.queue[0]

    def is_empty(self):
        return len(self.queue) == 0

    def measurement(self):
        print(f"Dimension: len(self.queue)")
        return len(self.queue)

    def clear(self):
        self.queue = []
        print("Queue cleared")

# Instance utilization
lq = ListQueue()
lq.enqueue(1)
lq.enqueue(2)
lq.peek()
lq.dequeue()
lq.measurement()
lq.clear()

Output:

Enqueued: 1
Enqueued: 2
Peek: 1
Dequeued: 1
Dimension: 1
Queue cleared

Utilizing collections.deque

The collections.deque class from the collections module gives a extra environment friendly option to implement a queue because it permits O(1) operations for appending and popping parts from each ends.

from collections import deque

class DequeQueue:
    def __init__(self):
        self.queue = deque()

    def enqueue(self, merchandise):
        self.queue.append(merchandise)
        print(f"Enqueued: merchandise")

    def dequeue(self):
        if self.is_empty():
            elevate IndexError("Dequeue from an empty queue")
        merchandise = self.queue.popleft()
        print(f"Dequeued: merchandise")
        return merchandise

    def peek(self):
        if self.is_empty():
            elevate IndexError("Peek from an empty queue")
        print(f"Peek: self.queue[0]")
        return self.queue[0]

    def is_empty(self):
        return len(self.queue) == 0

    def measurement(self):
        print(f"Dimension: len(self.queue)")
        return len(self.queue)

    def clear(self):
        self.queue.clear()
        print("Queue cleared")

# Instance utilization
dq = DequeQueue()
dq.enqueue(1)
dq.enqueue(2)
dq.peek()
dq.dequeue()
dq.measurement()
dq.clear()

Output:

Enqueued: 1
Enqueued: 2
Peek: 1
Dequeued: 1
Dimension: 1
Queue cleared

Utilizing queue.Queue

The queue.Queue class from the queue module is designed particularly for multi-threaded programming. It gives thread-safe queues and varied synchronization primitives.

from queue import Queue, Empty

class ThreadSafeQueue:
    def __init__(self, maxsize=0):
        self.queue = Queue(maxsize=maxsize)

    def enqueue(self, merchandise):
        self.queue.put(merchandise)
        print(f"Enqueued: merchandise")

    def dequeue(self):
        attempt:
            merchandise = self.queue.get(timeout=1)  # Await as much as 1 second for an merchandise
            print(f"Dequeued: merchandise")
            return merchandise
        besides Empty:
            elevate IndexError("Dequeue from an empty queue")

    def peek(self):
        with self.queue.mutex:
            if self.queue.empty():
                elevate IndexError("Peek from an empty queue")
            print(f"Peek: self.queue.queue[0]")
            return self.queue.queue[0]

    def is_empty(self):
        return self.queue.empty()

    def measurement(self):
        print(f"Dimension: self.queue.qsize()")
        return self.queue.qsize()

    def clear(self):
        with self.queue.mutex:
            self.queue.queue.clear()
            print("Queue cleared")

# Instance utilization
tsq = ThreadSafeQueue()
tsq.enqueue(1)
tsq.enqueue(2)
tsq.peek()
tsq.dequeue()
tsq.measurement()
tsq.clear()

Output:

Enqueued: 1
Enqueued: 2
Peek: 1
Dequeued: 1
Dimension: 1
Queue cleared

Functions of Queues

Queues are broadly utilized in varied functions, together with:

• Activity Scheduling: Pc scientists suggest the queue as one of many primary summary information sorts, which many functions use to order parts in keeping with a selected criterion.
• Breadth-First Search: One other traversal algorithm is the BFS algorithm which employs a queue information construction to traverse nodes in a graph degree by degree.
• Dealing with Asynchronous Information: It is because internet servers deal with information move by utilizing queues, processing requests within the order they obtain them.
• Buffering: Queues are simply as IO Buffers that relate information Interchange transactions as a option to management information move between information producers and information customers.
• Print Spooling: Scheduling of print jobs in printers who accomplish print requests on a first-come, first-served foundation.
• Order Processing: Prospects orders’ administration within the context of each bodily and on-line shops.
• Useful resource Allocation: Handle shared assets like printers or CPU time (e.g., allocate assets primarily based on queue place).
• Batch Processing: Deal with jobs in batches, processing them sequentially (e.g., picture processing, information evaluation).
• Networking: Handle community visitors, routing information packets (e.g., routers use queues to buffer incoming packets).
• Working Methods: Handle interrupts, deal with system calls, and implement course of scheduling.
• Simulations: Mannequin real-world programs with ready traces (e.g., financial institution queues, visitors lights).

Superior Queue Sorts

Allow us to now look into the superior queue sorts beneath:

Precedence Queue

A precedence queue assigns a precedence to every aspect. Parts with increased precedence are dequeued earlier than these with decrease precedence.

from queue import PriorityQueue

pq = PriorityQueue()

# Enqueue
pq.put((1, 'process 1'))  # (precedence, worth)
pq.put((3, 'process 3'))
pq.put((2, 'process 2'))

# Dequeue
print(pq.get())  # Output: (1, 'process 1')
print(pq.get())  # Output: (2, 'process 2')

Double-Ended Queue (Deque)

A deque permits parts to be added or faraway from each ends, making it extra versatile.

from collections import deque

deque = deque()

# Enqueue
deque.append(1)        # Add to rear
deque.appendleft(2)    # Add to entrance

# Dequeue
print(deque.pop())     # Take away from rear, Output: 1
print(deque.popleft()) # Take away from entrance, Output: 2

Round Queue

Effectively makes use of array area by wrapping round to the start when the top is reached.

class CircularQueue:
    def __init__(self, capability):
        self.queue = [None] * capability
        self.entrance = self.rear = -1
        self.capability = capability

    def is_empty(self):
        return self.entrance == -1

    def is_full(self):
        return (self.rear + 1) % self.capability == self.entrance

    def enqueue(self, merchandise):
        if self.is_full():
            print("Queue Overflow")
            return
        if self.entrance == -1:
            self.entrance = 0
        self.rear = (self.rear + 1) % self.capability
        self.queue[self.rear] = merchandise

    def dequeue(self):
        if self.is_empty():
            print("Queue Underflow")
            return
        merchandise = self.queue[self.front]
        if self.entrance == self.rear:
            self.entrance = self.rear = -1
        else:
            self.entrance = (self.entrance + 1) % self.capability
        return merchandise

    def peek(self):
        if self.is_empty():
            print("Queue is empty")
            return
        return self.queue[self.front]

    def measurement(self):
        if self.is_empty():
            return 0
        return (self.rear + 1 - self.entrance) % self.capability

# Instance utilization
cq = CircularQueue(5)
cq.enqueue(1)
cq.enqueue(2)
cq.enqueue(3)
print(cq.dequeue())  # Output: 1
print(cq.peek())  # Output: 2

Blocking Queue

It synchronizes entry between threads. It blocks when the queue is full or empty till area is out there.

import queue

class BlockingQueue:
    def __init__(self, maxsize):
        self.queue = queue.Queue(maxsize)

    def put(self, merchandise):
        self.queue.put(merchandise)

    def get(self):
        return self.queue.get()

    def empty(self):
        return self.queue.empty()

    def full(self):
        return self.queue.full()

# Instance utilization
bq = BlockingQueue(5)
import threading

def producer():
    for i in vary(10):
        bq.put(i)

def shopper():
    whereas True:
        merchandise = bq.get()
        print(merchandise)
        bq.task_done()

producer_thread = threading.Thread(goal=producer)
consumer_thread = threading.Thread(goal=shopper)
producer_thread.begin()
consumer_thread.begin()

Benefits of Queues

• Order Upkeep: Queues preserve the order of parts, which is important for process scheduling and processing sequences.
• Concurrency Dealing with: Queues effectively handle concurrent information processing, particularly in multi-threaded functions.
• Simplicity and Flexibility: You possibly can implement queues simply and adapt them for varied functions, from easy process administration to complicated information processing pipelines.

Conclusion

Pc scientists suggest the queue as one of many primary summary information sorts, which many functions use to order parts in keeping with a selected criterion. Queues are of various sorts in python however beneath are the most effective and generally used strategies to implement them. Studying the correct utilization of queues in addition to mastering their utility can play an intensive position in sprucing one’s programming expertise and make it doable to handle quite a few points.

Often Requested Questions