Queue In Python

In Python, The `queue` is a data structure that follows the FIFO (First In First Out) Approach and is used in programming for sorting. `queue` is one of the earliest data structures defined in computer science. we can implement a queue data structure using various approaches.

One common way is to use the deque class from the collections module, which provides efficient appending and popping from both ends of the queue.

Alternatively, we can use a list and implement the queue operations manually.

Here's an example of implementing a queue using deque:

Creating custom queue class from `collections` deque class

Example:

# import deque from collections module 
from collections import deque

# Declaring Custom Queue
class Queue:

    # constructor automatically invoked once, queue instance created.
    def __init__(self):
        self.queue = deque()

    # enqueue function to add item in the end of queue.
    def enqueue(self, item):
        self.queue.append(item)

    # queue function to get current size of queue.
    def size(self):
        return len(self.queue)

    def peek(self):
        if len(self.queue) == 0:
            return None
        return self.queue[0]

# queue instance created
q = Queue()

Add items within queue by calling enqueue function of Queue Class

Adding Items in queue using `enqueue()` method and checking size of queue using `size()` method

Example:

q.enqueue(1)
q.enqueue(2)
q.enqueue(3)

# checking queue size
print("Queue size:", q.size())  # Output: 3

Check Peek value in Queue

Checking Peek value in Queue else return None Data Type value

Example:

# print peek value in queue else peek function will return None Data Type value
print("Front of the queue:", q.peek())  # Output: 1

Remove Elements from Queue

Define dequeue method inside Queue Class. dequeue() removes and returns the first item from the list (the leftmost element), simulating the behaviour of a queue.

Example:

def dequeue(self):
   if len(self.queue) == 0:
      return None
   return self.queue.popleft()

Print data from queue

we need to define the `is_empty()` method in the Queue class, to validate that the queue is not empty before iterating.

After creating an instance of the queue, we can print queue items using the `while` keyword.

Example:

# queue function to check is queue empty.
  def is_empty(self):
    return len(self.queue) == 0


# After creating an instance of the queue, checking if queue is not empty then, print its items.
while not q.is_empty():
    # Printing values of queue.
    print(q.dequeue())  # Output: 1, 2, 3

Full Code:

# import deque from collections module 
from collections import deque

# Declaring Custom Queue
class Queue:

    # constructor automatically invoked once, queue instance created.
    def __init__(self):
        self.queue = deque()

    # enqueue function to add item in the end of queue.
    def enqueue(self, item):
        self.queue.append(item)

    def dequeue(self):
        if len(self.queue) == 0:
            return None
        return self.queue.popleft()

    # queue function to get current size of queue.
    def size(self):
        return len(self.queue)

    # queue function to check is queue empty.
    def is_empty(self):
        return len(self.queue) == 0

    def peek(self):
        if len(self.queue) == 0:
            return None
        return self.queue[0]

# queue instance created
q = Queue()

# adding items within queue by calling enqueue function of Queue Class.
q.enqueue(1)
q.enqueue(2)
q.enqueue(3)

# checking queue size
print("Queue size:", q.size())  # Output: 3

# print peek value in queue else peek function will return None Data Type value
print("Front of the queue:", q.peek())  # Output: 1

print("Dequeueing elements:")

# Checking if queue is not empty then, print its items.
while not q.is_empty():
    # Printing values of queue.
    print(q.dequeue())  # Output: 1, 2, 3

Note:

"enqueue(item)" adds an item to the end of the list.
"dequeue()" removes and returns the first item from the list (the leftmost element), simulating the behaviour of a queue.
"size()" returns the current size of the queue.
"is_empty()" checks if the queue is empty.
"peek()" checks the peek value in a queue using the "peek" method.

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