It might be better to pick a better (but probably platform-specific) API
for such a use-case.  os.kill has a problem with false positives (on
Linux it will tell you a process exists even when it doesn't).  Looking
in /proc/ or using a Windows API to enumerate all existing processes
might be better.  These have the advantage of giving you a bunch of PID
information all at once which you can then check against, rather than
repeatedly making syscalls.