Mark Dickinson added the comment: I just noticed this point, which may be confusing things:

Rebut: order is undefined, concurrent_futures specifies map() returns an iterator, where builtin map returns a list.

In Python 3, the built-in map function returns an iterator, not a list. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue26374> _______________________________________