killall tor && service tor start in Python

what is different between  

subprocess.Popen

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 and

subprocess.call

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If you use subprocess.Popen, then the process is started, but python does not wait for it to be finished.

The equivalen with subprocess Popen would be.

import subprocess
proc1 = subprocess.Popen(["killall", "tor"])
returncode = proc1.wait()
if returncode == 0:
    proc2 = subprocess.Popen(["service", "tor", "start"])
    returncode = proc2.wait()

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subprodcess.call() is just a shortcut.

if you use subprocess Popen without the wait function, then you might call
"service tor start" before "killall tor" has been finished.
and the python script would continue executing other python commands before any of the subprocesses had been finished.