How do I parallelize a simple Python loop?

Question

This is probably a trivial question, but how do I parallelize the following loop in python?

# setup output lists
output1 = list()
output2 = list()
output3 =          


        

Answer 1

Using multiple threads on CPython won't give you better performance for pure-Python code due to the global interpreter lock (GIL). I suggest using the multiprocessing module instead:

pool = multiprocessing.Pool(4)
out1, out2, out3 = zip(*pool.map(calc_stuff, range(0, 10 * offset, offset)))

Note that this won't work in the interactive interpreter.

To avoid the usual FUD around the GIL: There wouldn't be any advantage to using threads for this example anyway. You want to use processes here, not threads, because they avoid a whole bunch of problems.