{{tag>Brouillon Python CA}}

= Python - callback

Voir :
* [[Notes Python multithreading]]

== Introduction

Exemple d'une fonction sans callback
<code python>
#! /usr/bin/env python3

from functools import reduce


def calcfact(i):
    assert i >= 0
    return reduce(lambda a, b: a * b, range(1, i+1) if i > 1 else [1])


print(calcfact(3))
</code>

Exemple de la même fonction avec callback optionnel
<code python>
#! /usr/bin/env python3

from functools import reduce


def calcfact_called(i, res):
    print(i, '! = ', res, sep='')


def calcfact(i, callback=None):
    assert i >= 0
    res = reduce(lambda a, b: a * b, range(1, i+1) if i > 1 else [1])
    if callback is None:
        return res
    else:
        callback(i, res)

# Sans Callback
print(calcfact(3))

# Avec Callback
calcfact(4, calcfact_called)
</code>



== Exemple avec async / asyncio / await

<code python>
#! /usr/bin/env python3
 
import asyncio


def waitplop_called(i):
    print(i)


async def waitplop(i, callback=None):
    await asyncio.sleep(i)
    if callback is None:
        return i
    else:
        callback(i)


async def main():
    async with asyncio.TaskGroup() as tg:
        # Asynchronous with callback
        tg.create_task(waitplop(3, waitplop_called))
        tg.create_task(waitplop(3, waitplop_called))

        # Synchronous / sequential without callback
        task1 = await tg.create_task(waitplop(4))
        print(task1)


asyncio.run(main())
</code>

<code ->
$ time ./plop.py 
3
3
4

real    0m4.120s
user    0m0.095s
sys     0m0.024s
</code>

=== Autre façon de faire un callback avec asyncio

Voir : 
* https://www.youtube.com/watch?v=gn6qo3k97hM

<code python>
#! /usr/bin/env python3
 
import asyncio


def waitplop_called(task):
    print(task.result())


async def waitplop(i):
    await asyncio.sleep(i)
    return i


async def main():
     task = asyncio.create_task(waitplop(3))
     task.add_done_callback(waitplop_called)
     await asyncio.gather(task)


asyncio.run(main())
</code>


== Autres

Voir : 
* https://docs.python.org/fr/3/library/asyncio-future.html

<code python>
# Call 'print("Future:", fut)' when "fut" is done.
fut.add_done_callback(
    functools.partial(print, "Future:"))
</code>