How to Use Python List as Queue

In programming, a queue is a data structure that stores elements in a First-In, First-Out (FIFO) order. Python provides several ways to implement a queue, but one of the most straightforward ways is by using a list. In this tutorial, we’ll explore how to use Python lists as a queue and show some coding examples.

Using Python List as Queue

1. Using append() and pop(0) methods:

A simple way to use a Python list as a queue is by using the append() method to add items to the end of the list, and pop(0) to remove items from the beginning.

queue = []
queue.append(10)
queue.append(20)
queue.append(30)
print(queue)  # Output: [10, 20, 30]

item = queue.pop(0)
print(item)   # Output: 10
print(queue)  # Output: [20, 30]

However, using pop(0) on a list is not efficient, as it shifts all the elements one position, leading to an (O(n)) time complexity.

2. Using collections.deque:

A more efficient way to implement a queue in Python is by using the collections.deque class, which provides (O(1)) time complexity for append and pop operations.

from collections import deque

queue = deque()
queue.append(10)
queue.append(20)
queue.append(30)
print(queue)  # Output: deque([10, 20, 30])

item = queue.popleft()
print(item)   # Output: 10
print(queue)  # Output: deque([20, 30])

3. Using queue module:

Python also provides a queue module specifically designed for queue operations. This can be particularly useful in multithreading environments.

from queue import Queue

queue = Queue()
queue.put(10)
queue.put(20)
queue.put(30)

item = queue.get()
print(item)   # Output: 10

Conclusion

While Python lists can be used to implement a queue, it is generally more efficient to use a collections.deque or the queue module. If you need to implement a basic queue and are not concerned with efficiency, using append() and pop(0) with a list will suffice. Otherwise, consider using collections.deque or the queue module to benefit from optimized performance.