Pythonic way to detach a process?

To implement sh's &, avoid cargo cult programming and use subprocess module directly:

import subprocess

etcd = subprocess.Popen('etcd') # continue immediately
next_cmd_returncode = subprocess.call('next_cmd') # wait for it
# ... run more python here ...
etcd.terminate() 
etcd.wait()

This ignores exception handling and your talk about "daemon mode" (if you want to implement a daemon in Python; use python-daemon. To run a process as a system service, use whatever your OS provides or a supervisor program such as supervisord).

Author of sh here. I believe you want to use the _bg special keyword parameter http://amoffat.github.io/sh/#background-processes

This will fork your command and return immediately. The process will continue to run even after your script exits.