The problem I have with the solution that is currently implemented is that subprocess is waiting for the spawned child although the child is not running anymore.
In my case this issue occured when invoking samba or the small sample daemon (see attached file above).
For example, invoking the daemon from a bash, the daemon program exits immediately and its spawned child is running in the background. The point is that the bash is accessible right after starting the daemon. It is not waiting for the daemon process in the background to close the open pipe.

What do you think of using a waitpid for this scenario?
subprocess.Popen could wait for the pid of the daemon starter and gets back control once the pid of the daemon starter is gone. This way, subprocess.Popen does not need to wait for EOF on left-open pipes.