How to unpack generator results from ProcessPoolExecutor?

Question

I am trying to use ProcessPoolExecutor to initiate multiple instances of a class (BT), which initiates a method BT.bt(), and return results [aList1, aList2].

I have tried to package info which is required by each instance of the class into a simple iterator (bulkInfo). The iterator is then thrown to each instance of the class and executed. As I understand it, the results should be a generator or a list, with each result (combiList) in results being a list of 2 'minilists' [aList1, aList2].

However I cannot unpack the results. Or more correctly, I cannot unpack each result in results. Pycharm highlights warnings at result[0] and result[1] — Class 'BT' does not define '__getitem__', so the [] operator cannot be used on its instances.

Running the code as is gives error TypeError: 'list' object is not callable. The full version of the code gives error TypeError: cannot pickle 'generator' object.

How to unpack each result in results to give me miniList1 and miniList2?

The code below is a stripped back version to outline the problem. I have tried using yield instead of return combiList. I have tried throwing results to list(results) and iterating through each result. I have tried many variations of packing the bulkinfo iterator as a list of lists or a list of tuples. I have tried defining combiList as a list and as a tuple. I have tried list(results) followed by list(result) to access each miniList.

import concurrent.futures as cf
import numpy as np

class BT:
    def __init__(self, bulkInfo):
        self.aCyc = bulkInfo(3)
        self.bt(self.aCyc)

    def bt(self, aCycle):
        aList1 = []
        aList2 = []
        someInfo = [aCycle, 'bunch', 'of', 'stuff']
        [aList1.append(s) for s in someInfo]
        [aList2.append(s) for s in someInfo]
        combiList = [aList1, aList2]
        return combiList

if __name__ == '__main__':
    dummy1 = 'something'
    cycles = np.arange(10)
    bulkInfo = []
    [bulkInfo.append([dummy1, dummy1, dummy1, aCyc]) for aCyc in cycles]

    with cf.ProcessPoolExecutor(max_workers=4) as executor:
        results = executor.map(BT, bulkInfo)

        for result in results:
            miniList1 = result[0]
            miniList2 = result[1]

        # for result in list(results):
        #     for miniList in list(result):
        #         print(miniList)

I am not so concerned with performance, but just trying to get the results out of the ProcessPoolExecutor. So I simply want output results as a list, but perhaps it is a generator (It is not clear to me here when lists are "becoming" generators, or vice versa. I just want to extract miniList1 and miniList2.)

Answer 1

        with concurrent.futures.ProcessPoolExecutor() as executor:
        results = executor.map(self._translate, itertools.repeat(text), languages)
        rlist = []
        for res in results:
            rlist.append(res)
            # print(type(res))
        return rlist

you can create list and append it like here rlist.append(res)