Python Using List/Multiple Arguments in Pool Map

Question

I am trying to pass a list as a parameter to the pool.map(co_refresh, input_list). However, pool.map didn\'t trigger the function co_refresh

Answer 1

Consider the below code

from multiprocessing.pool import Pool

data = [["a1", "b1", "c1", "d1"],
        ["a2", "b2", "c2", "d2"],
        ["a3", "b3", "c3", "d3"], ]


def someaction(a, b=1, c=2, d=3):
    print(a, b, c, d)

When you call this in your script using a pool

pool = Pool(4)
pool.map(someaction, data)

The output is

['a1', 'b1', 'c1', 'd1'] 1 2 3
['a2', 'b2', 'c2', 'd2'] 1 2 3
['a3', 'b3', 'c3', 'd3'] 1 2 3

So a gets the array and rest all parameters are not passed. Pool.map expects a function to only have one argument. So for your case to work you need to create a wrapper function

def someaction_wrapper(data):
    someaction(*data)

And then call this wrapper function in pool. Now you use

pool = Pool(4)
pool.map(someaction_wrapper, data)

And the output is

a1 b1 c1 d1
a2 b2 c2 d2
a3 b3 c3 d3

Which is what you wanted I believe