Multithreading and mapping multiple variables

Question

I am trying to figure out how to do multithreading in Python, namely how to use the map function to call my function with multiple variables.

My code:

from multiprocessing.dummy import Pool as ThreadPool 
def myFunc(a, b):
    print(a * b)

arr = [4, 8, 10, 7, 9]
arr2 = [2, 1, 3, 4, 2]

pool = ThreadPool(4) 

results = pool.map(myFunc, arr, arr2)

pool.close() 
pool.join() 

It get the following error from the pool.map function call:

TypeError: '<=' not supported between instances of 'list' and 'int'

Which I don't quite get. From the documentation I should be able to do this.

What am I missing?

Answer 1

Here is an example. The built-in map can take more than two iterators, but for pool.map, it can take only one iterator as the second argument.

from multiprocessing import Pool

def myFunc(x):
    print(x[0] * x[1])

arr = [4, 8, 10, 7, 9]
arr2 =[2, 1, 3, 4, 2]

if __name__ == '__main__':

    pool = Pool(4)
    results = pool.map(myFunc, zip(arr, arr2))

    pool.close() 
    pool.join()

Please compare the followings for more detail.

https://docs.python.org/3.6/library/multiprocessing.html#multiprocessing.pool.Pool.map https://docs.python.org/3/library/functions.html#map