python - Multiprocessing : use tqdm to display a progress bar

Question

To make my code more "pythonic" and faster, I use "multiprocessing" and a map function to send it a) the function and b) the range of iterations.

The implanted solution (i.e., call tqdm directly on the range tqdm.tqdm(range(0, 30)) does not work with multiprocessing (as formulated in the code below).

The progress bar is displayed from 0 to 100% (when python reads the code?) but it does not indicate the actual progress of the map function.

How to display a progress bar that indicates at which step the 'map' function is ?

from multiprocessing import Pool
import tqdm
import time

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
   p = Pool(2)
   r = p.map(_foo, tqdm.tqdm(range(0, 30)))
   p.close()
   p.join()

Any help or suggestions are welcome...

Answer 1

Use imap instead of map, which returns an iterator of processed values.

from multiprocessing import Pool
import tqdm
import time

def _foo(my_number):
   square = my_number * my_number
   time.sleep(1)
   return square 

if __name__ == '__main__':
   with Pool(2) as p:
      r = list(tqdm.tqdm(p.imap(_foo, range(30)), total=30))