Cannot modify global variable

[gtimoshaz]

I have the following code:

import p_tqdm
d = dict()

def modify_dict(a):
    d[a] = a ** 2

p_tqdm.p_map(modify_dict, list(range(10)))
print(d)

It outputs {} instead of {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}.

In comparasion, concurrent.futures works as expected:

import concurrent.futures
with concurrent.futures.ThreadPoolExecutor(max_workers=50) as executor:
     executor.map(modify_dict, list(range(10)))

[gtimoshaz]

Found a workaround: use dicts from multiprocessing.Manager()

import multiprocessing
manager = multiprocessing.Manager()
shared_dict = manager.dict()

def modify_dict(a):
    shared_dict[a] = a ** 2

p_tqdm.p_map(modify_dict, list(range(10)))
print(shared_dict)

The output is {1: 1, 0: 0, 2: 4, 7: 49, 4: 16, 8: 64, 3: 9, 6: 36, 5: 25, 9: 81} (the order might be different)

This is, however, just a workaround. Python dicts are thread-safe, and there are no reason why can't one use it with this library. However, the problem might belong to the dependency, pathos