Python 3: does Pool keep the original order of data passed to map?

Pool.map results are ordered. If you need order, great; if you don't, Pool.imap_unordered may be a useful optimization.

Note that while the order in which you receive the results from Pool.map is fixed, the order in which they are computed is arbitrary.

The documentation bills it as a "parallel equivalent of the map() built-in function". Since map is guaranteed to preserve order, multiprocessing.Pool.map makes that guarantee too.