lesson05_future_callback.py

# SuperFastPython.com
# example of adding a done callback to a task
from time import sleep
from concurrent.futures import ProcessPoolExecutor

# callback function to call when a task is completed
def custom_callback(future):
 # report a message
 print(f'Custom callback got: {future.result()}',
 flush=True)

# custom task function executed in a worker process
def work():
 # block for a moment
 sleep(1)
 # return a result
 return 99

# protect the entry point
if __name__ == '__main__':
 # create a process pool
 with ProcessPoolExecutor() as exe:
 # execute the task
 fut = exe.submit(work)
 # add the custom callback
 fut.add_done_callback(custom_callback)