queue

The queue module is a standard library in Python.

The queue module provides the following classes:

• queue.Queue(maxsize=0): A first-in, first-out (FIFO) queue.

• queue.LifoQueue(maxsize=0): A last-in, first-out (LIFO) queue.

• queue.PriorityQueue(maxsize=0): A priority queue.

In these classes, the maxsize parameter is an integer that sets the maximum number of items that can be placed in the queue. If maxsize is less than or equal to zero, the queue size is infinite.

queue.Queue

The queue.Queue class is a FIFO queue.

import queue

q = queue.Queue(maxsize=3)
q.put(1)
q.put(2)
q.put(3)
print('Queue full:', q.full())
print('Queue empty:', q.empty())

print(q.get())
print(q.get())
print(q.get())
print('Queue empty:', q.empty())

queue.LifoQueue

queue.PriorityQueue

The queue.PriorityQueue class is a priority queue.

In the priority queue, the lowest value is retrieved first.　A typical pattern for entries is a tuple in the form (priority_number, data).

import queue

q = queue.PriorityQueue(maxsize=0)
q.put((2, 'b'))
q.put((1, 'a'))
q.put((3, 'c'))
q.put((4, 'd'))

while not q.empty():
    print(q.get())

(1, 'a')
(2, 'b')
(3, 'c')
(4, 'd')