determine if os.system() is done

[Xah Lee]

suppose i'm calling two system processes, one to unzip, and one to
“tail” to get the last line. How can i determine when the first
process is done?

Example:

subprocess.Popen([r"/sw/bin/gzip","-d","access_log.4.gz"]);

last_line=subprocess.Popen([r"/usr/bin/tail","-n 1","access_log.4"],
stdout=subprocess.PIPE).communicate()[0]

of course, i can try workarounds something like os.system("gzip -d
thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
determine when a system process is done.

 Xah
 xah at xahlee.org
∑ http://xahlee.org/