What is Queue Data Structure In Python?

Queue Data Structure In Python

The primary queue operations are as follows:

Enqueue: It adds an element to the end of the queue. When the queue reaches its total capacity, it reaches an overflow condition. The time complexity of enqueueing is O:1.

Dequeue: This operation removes an element from the queue. Since it bases the queue on a FIFO manner, it releases the items in the order of their additions. When the queue becomes empty, it reaches an underflow condition. The time complexity is O:1.

Front: It gives you the first item from the queue. The time complexity is O:1.

Rare: It gives you the last item from the queue. The time complexity is O:1.

What are the Methods Available for Queue in Python?

There are numerous methods available in Python to perform operations on the queue. Some of the standard methods are:

put(item): Inserts an element to the queue

get(): Gets an element from the queue

empty(): Checks and returns true if the queue is empty

qsize: Returns queue’s length

full(): Checks and returns true if the queue is full

maxsize(): Maximum elements allowed in a queue

How to Implement Queue in Python?

There are different ways to implement a queue in Python. Some common ways to implement a queue include:

list

collections.deque

collections.Queue

Example: Implementing a Queue in Python with a List

Python list is used as a way of implementing queues. The list’s append() and pop() methods can insert and delete elements from the queue. However, while using this method, shift all the other elements of the list by one to maintain the FIFO manner. This results in requiring O(n) time complexity. The example below demonstrates a Python queue using a list.

# Initialize a queue

queue_exm = []

# Adding elements to the queue

queue_exm.append(‘x’)

queue_exm.append(‘y’)

queue_exm.append(‘z’)

print(“Queue before any operations”)

print(queue_exm)

# Removing elements from the queue

print(“\nDequeuing items”)

print(queue_exm.pop(0))

print(queue_exm.pop(0))

print(queue_exm.pop(0))

print(“\nQueue after deque operations”)

print(queue_exm)

Output:

/QueueinPython_1

Example: Implementing a Queue in Python with collections.deque

Collections.deque provides the same O(1) time complexity as queues. Hence, it implements a queue, and performs append() & pop() functions quicker than lists. For performing enqueuing and dequeuing using collections.deque, append() and popleft() functions are used.

From collections import deque

queue_exm = deque()

queue_exm.append(‘x’)

queue_exm.append(‘y’)

queue_exm.append(‘z’)

print(“Queue before operations”)

print(queue_exm)

# Dequeuing elements

print(“\nDequeuing elements”)

print(queue_exm.popleft())

print(queue_exm.popleft())

print(queue_exm.popleft())

print(“\nQueue after operations”)

print(queue_exm)

Output:

QueueinPython_2

Example: Implementing a Queue in Python with the queue.Queue

It is an in-built module for implementing a queue in Python. You can use different functions available in the module to perform operations on a queue. Below is an example of implementing a queue with the help of a queue, along with the use of different functions.

From queue import Queue

queue_exm = Queue(maxsize = 3)

print(queue_exm.qsize())

# Adding of element to queue

queue_exm.put(‘x’)

queue_exm.put(‘y’)

queue_exm.put(‘z’)

print(“Full: “, queue_exm.full())

print(“Dequeuing elements”)

print(queue_exm.get())

print(queue_exm.get())

print(queue_exm.get())

print(“Empty: “, queue_exm.empty())

queue_exm.put(1)

print(“Empty: “, queue_exm.empty())

print(“Full: “, queue_exm.full())

Output:

QueueinPython_3.

How to Add Elements to a Queue in Python?

You can add elements to a Python queue from the rear end. The process of adding elements is known as enqueuing. Depicted below is an example to understand it. In this example, you will create a Queue class and use the insert method to implement a FIFO queue.

# Creating the queue class

class Queue:

def __init__(self):

self.queue = list()

def element_add_exm(self,data):

# Using the insert method

if data not in self.queue:

self.queue.insert(0,data)

return True

return False

def leng(self):

return len(self.queue)

Queue_add = Queue()

Queue_add.element_add_exm(“Mercedes Benz”)

Queue_add.element_add_exm(“BMW”)

Queue_add.element_add_exm(“Maserati”)

Queue_add.element_add_exm(“Ferrari”)

Queue_add.element_add_exm(“Lamborghini”)

print(“Queue’s Length: “,Queue_add.leng())

Output:

QueueinPython_4

How to Remove Elements From a Queue in Python?

You can also remove an element from a queue, and that process is called dequeuing. Use the built-in pop() function in the below example to see how to remove an element from the queue. In this code, you will create a Queue class and then define two methods: to add elements and delete them. You will then check the underflow status of the queue (if it’s empty). When it returns false, you will start removing the elements one-by-one.

# Creating the queue class

class Queue:

def __init__(self):

self.queue = list()

def element_add_exm(self,data):

# Using the insert method

if data not in self.queue:

self.queue.insert(0,data)

return True

return False

# Removing elements

def element_remove_exm(self):

if len(self.queue)>0:

return self.queue.pop()

return (“Empty Queue”)

queu = Queue()

queu.element_add_exm(“A”)

queu.element_add_exm(“B”)

queu.element_add_exm(“C”)

queu.element_add_exm(“D”)

print(queu)

print(queu.element_remove_exm())

print(queu.element_remove_exm())

Output:

QueueinPython_5

How to Sort a Python Queue?

You can also sort a queue in Python using for loops. Here’s an example to better understand it. In the code below, you will use two for loops to sort a queue having integer values.

import queue

queu = queue.Queue()

queu.put(5)

queu.put(24)

queu.put(16)

queu.put(33)

queu.put(6)

# Using bubble sort algorithm for sorting

i = queu.qsize()

for x in range(i):

# Removing elements

n = queu.get()

for j in range(i-1):

# Removing elements

y = queu.get()

if n > y :

# putting smaller elements at beginning

queu.put(y)

else:

queu.put(n)

n = y

queu.put(n)

while (queu.empty() == False):

print(queu.queue[0], end = ” “)

queu.get()

Output:

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