is synchronization needed with multiprocessor in python?

when using a code like this

def execute_run(list_out): 
   ... do something 

pool = ThreadPoolExecutor(6)
for i in list1:
    for j in list2:
            pool.submit(myfunc, list_out)
pool.join()

assuming the threads modify list_out, do they do that in a synchronous manner?

If your goal is calculate something in multiprocessing way, it's better do not share state. I propose you to use simple map from multiprocessing if it's possible:

from multiprocessing import Pool

input_list = []
for i in list1:
    for j in list2:
        input_list.append((i, j))

p = Pool()
result_list = p.map(do_something, input_list)

map works like for-loop:

def naive_map(input_list, do_something):
   result = []
   for i in input_list:
     result.append(do_something(i))
   return result

So, if you want to use function that is accepting several arguments, you can use lambda function for unpacking tuple.

  >> def your_function(v1, v2):
  >>        return v1+v2
  >> f = lambda (x,y): your_function(x, y)
  >> map(f, [(1,2),(3,4),(5,6)])
       [3, 7, 11]