# 18.5.8. Queues

Source code: Lib/asyncio/queues.py

Queues:

- `Queue`

- `PriorityQueue`

- `LifoQueue`

asyncio queue API was designed to be close to classes of the `queue` module (`Queue`, `PriorityQueue`, `LifoQueue`), but it has no timeout parameter. The `asyncio.wait_for()` function can be used to cancel a task after a timeout.

## 18.5.8.1. Queue

class `asyncio.``Queue`(maxsize=0, *, loop=None)

  A queue, useful for coordinating producer and consumer coroutines.

  If maxsize is less than or equal to zero, the queue size is infinite. If it is an integer greater than `0`, then `yield from put()` will block when the queue reaches maxsize, until an item is removed by `get()`.

  Unlike the standard library `queue`, you can reliably know this Queue’s size with `qsize()`, since your single-threaded asyncio application won’t be interrupted between calling `qsize()` and doing an operation on the Queue.

  This class is not thread safe.

  Modifié dans la version 3.4.4: Les nouvelles méthodes `join()` et `task_done()`.

  `empty`()

    Renvoie `True` si la queue est vide, `False` sinon.

  `full`()

    Return `True` if there are `maxsize` items in the queue.

    Note

    If the Queue was initialized with `maxsize=0` (the default), then `full()` is never `True`.

  coroutine `get`()

    Remove and return an item from the queue. If queue is empty, wait until an item is available.

    Cette méthode est une coroutine.

    Voir aussi

    La méthode `empty()`.

  `get_nowait`()

    Supprime et donne un élément de la queue.

    Return an item if one is immediately available, else raise `QueueEmpty`.

  coroutine `join`()

    Bloque jusqu’à ce que tous les éléments de la queue aient été récupérés et traités.

    The count of unfinished tasks goes up whenever an item is added to the queue. The count goes down whenever a consumer thread calls `task_done()` to indicate that the item was retrieved and all work on it is complete. When the count of unfinished tasks drops to zero, `join()` unblocks.

    Cette méthode est une coroutine.

    Nouveau dans la version 3.4.4.

  coroutine `put`(item)

    Put an item into the queue. If the queue is full, wait until a free slot is available before adding item.

    Cette méthode est une coroutine.

    Voir aussi

    La méthode `full()`.

  `put_nowait`(item)

    Ajoute un élément dans la queue sans bloquer.

    If no free slot is immediately available, raise `QueueFull`.

  `qsize`()

    Nombre d’éléments dans la queue.

  `task_done`()

    Indicate that a formerly enqueued task is complete.

    Used by queue consumers. For each `get()` used to fetch a task, a subsequent call to `task_done()` tells the queue that the processing on the task is complete.

    If a `join()` is currently blocking, it will resume when all items have been processed (meaning that a `task_done()` call was received for every item that had been `put()` into the queue).

    Raises `ValueError` if called more times than there were items placed in the queue.

    Nouveau dans la version 3.4.4.

  `maxsize`

    Nombre d’éléments autorisés dans la queue.

## 18.5.8.2. PriorityQueue

class `asyncio.``PriorityQueue`

  A subclass of `Queue`; retrieves entries in priority order (lowest first).

  Entries are typically tuples of the form: (priority number, data).

## 18.5.8.3. LifoQueue

class `asyncio.``LifoQueue`

  A subclass of `Queue` that retrieves most recently added entries first.

### 18.5.8.3.1. Exceptions

exception `asyncio.``QueueEmpty`

  Exception raised when the `get_nowait()` method is called on a `Queue` object which is empty.

exception `asyncio.``QueueFull`

  Exception raised when the `put_nowait()` method is called on a `Queue` object which is full.