A minimal reproducible example to show asynchronous behavior using callbacks in Python-CodePudding

Background: To me it seems clear, that the conecpt of callbacks is flexible, but I also thought, it makes code much faster. However, the following example works, but it cannot show that time can be saved using a callback Ref1:

import time
from time import sleep

def callbackFunc(delay):
  time.sleep(delay)
  print("callback:     message 3 delay "   str(delay))

def saysomething(delay, callback):
  print("saysomething: message 2 delay "   str(delay))
  callback(delay) # hier muss ich schon wissen, dass nur "delay" benötigt wird...
  time.sleep(2)

if __name__ == '__main__':
  t0 = time.time()
  print("main:         message 1.")
  saysomething(2, callbackFunc)
  print("main:         message 4.")
  print("\ntime: ",time.time() - t0)

Output

main:         message 1.
saysomething: message 2 delay 2
callback:     message 3 delay 2
main:         message 4.
time:  4.01

So how can I achive something like this

main:         message 1.
saysomething: message 2 delay 2
callback:     message 3 delay 2
main:         message 4.
time:  2  !!!!!!!!!!!!!

Perhaps it was even possible to switch the order of messages 3 & 4? Or do I get anything wrong?

Perhaps, these answers here and here and the following code from here which does not use callbacks but shows asynchronous behavior help?

CodePudding user response：

This is irrelevant w.r.t. the SWIG callbacks used by the routing library.

CodePudding user response：

sleep() suspends execution of the calling thread, so you can't call it on the main thread if you want to show asynchronous behaviour.

You can use threads or the built-in event loop to show asynchronous behaviour.

Here's an example using the built-in event loop:

import asyncio
import time
# from time import sleep  # -


def callbackFunc(delay):
    # time.sleep(delay)                                                                               # -
    # print("callback:     message 3 delay "   str(delay))                                            # -
    asyncio.get_event_loop().call_later(delay, print, "callback:     message 3 delay "   str(delay))  #  


def saysomething(delay, callback):
    print("saysomething: message 2 delay "   str(delay))
    callback(delay)  # hier muss ich schon wissen, dass nur "delay" benötigt wird...
    # time.sleep(2)                                       # -
    asyncio.get_event_loop().call_later(2, lambda: None)  #  


def run_until_complete(loop):                                                             #  
    loop.call_soon(lambda: run_until_complete(loop) if loop._scheduled else loop.stop())  #  
    if not loop.is_running():                                                             #  
        loop.run_forever()                                                                #  


if __name__ == '__main__':
    t0 = time.time()
    print("main:         message 1.")
    saysomething(2, callbackFunc)
    print("main:         message 4.")
    run_until_complete(asyncio.get_event_loop())  #  
    print("\ntime: ", time.time() - t0)

Output:

main:         message 1.
saysomething: message 2 delay 2
main:         message 4.
callback:     message 3 delay 2

time:  2.000