Making parallel code work in python 2.7 and 3.6

Question

I have some code in python 3.6 which is like this:

from multiprocessing import Pool
with Pool(processes=4) as p:
    p.starmap(parallel_function, list(dict_variables.items()))

Here dict_variables looks like this:

[('aa', ['ab', 'ab', 'ad']), ('aa1', ['a1b', 'a1b', 'a2d'])]

This code only works in python 3.6. How can I make it work in 2.7?

Older versions of Python weren't built to be able to process that kind of code. You can only convert old code for newer builds (most of the time) — liam, Aug 04 '17 at 18:42

score 1 · Accepted Answer · answered Aug 04 '17 at 18:56

starmap was introduced in Python3.3. In Python2, use Pool.map and unpack the argument yourself:

In Python3:

import multiprocessing as mp

def starmap_func(x, y):
    return x**y

with mp.Pool(processes=4) as p:
    print(p.starmap(starmap_func, [(1,2), (3,4), (5,6)]))
    # [1, 81, 15625]

In Python2 or Python3:

import multiprocessing as mp

def map_func(arg):
    x, y = arg
    return x**y

p = mp.Pool(processes=4)
print(p.map(map_func, [(1,2), (3,4), (5,6)]))
# [1, 81, 15625]
p.close()

Making parallel code work in python 2.7 and 3.6

1 Answers1