I am learning how to run simple function on multiple threads in Python.

Assume this simple code:

from itertools import product

all_combinations = []

for cas in range(3):

    target_sum = 10

    combinations = product(range(target_sum + 1), repeat=4)

    valid_combinations = [combo for combo in combinations if sum(combo) == target_sum]

    all_combinations.append(valid_combinations)


compute_combo = []


for a in all_combinations[2]:
    for b in all_combinations[1]:
        for c in all_combinations[0]:
            compute_combo.append([a, b, c])




def foo(bar):
    max_combo = 0
    for j in bar:
        for a in j:
            suma = a[0] + a[1] + 3*a[2] + a[3]
            if suma > max_combo:
                max_combo = suma
    return max_combo

import time

start_time_simple = time.time()



result_simple = foo(compute_combo)

print(f"1 CPU result: {result_simple}")

end_time_simple = time.time()

execution_time_simple = end_time_simple - start_time_simple
print(f"1 CPU run time: {execution_time_simple} s")

This is how I try to run the foo() function on multiple threads:

from multiprocessing.dummy import Pool as ThreadPool

start_time_par = time.time()

pool = ThreadPool(4)

result_par = pool.map(foo, [compute_combo])

pool.close()
pool.join()

end_time_par = time.time()

execution_time_par = end_time_par - start_time_par

print(f"4 CPUs result {result_par}")

print(f"4 CPUs run time: {execution_time_par} s")

But the run time is the same, what is the problem here, please? Thanks a lot