data in without_initializer_worker_wrapper is a pair of the varying data and the auxiliary data. So, on line 48, data is being splat into two elements; compare with line 24.

If data were a 1000 element list, then the call on line 48 would fail due to function signature mismatch; see line 8.

If line 48 was changed to return worker(data, None), then no auxiliary data is passed to workers, which is a different kind of problem than what is being tackled in this post; see the start of the second paragraph of the post.

So, may be, you misunderstood the original post. Or, you did not express your concern correctly.