スレッドに依存せずに Python で真の並列 Bash プロセス実行を実現するにはどうすればよいですか?

<code class="python">from subprocess import Popen

commands = ['date; ls -l; sleep 1; date', ...]
processes = [Popen(cmd, shell=True) for cmd in commands]</code>

<code class="python">from functools import partial
from multiprocessing.dummy import Pool
from subprocess import call

pool = Pool(2)
for i, returncode in enumerate(pool.imap(partial(call, shell=True), commands)):
    ...</code>

<code class="python">from subprocess import Popen
from itertools import islice

max_workers = 2
processes = (Popen(cmd, shell=True) for cmd in commands)
running_processes = list(islice(processes, max_workers))
while running_processes:
    ...</code>