How to get a return while running under subprocess.Popen

Hello again,

I am running WinSCP in Python through subprocess.Popen and transferring files to a server.
Since this transfer takes a long while (the files are quite large), it sometimes interrupts the following commands, because the transfer is not yet done.
Is there a way to get a ping/return so to see that the process is finished? I am not running it as an executable for that matter.
Thanks a lot.
Merlin

This looks like a Python question, not WinSCP.
Anyway, what about this?
Is there a way to check if a subprocess is still running?