I would like to be able to call two (or more) commands within python but I would like to make sure that the first is finished before the second starts. Is that possible with subprocess? For example:
subprocess.call("script1 input1 > out", shell=True)
and when that command finishes:
subprocess.call("script2 out>out2", shell=True)
or is there a better way?
A call to subprocess.call blocks until the command completes. From the documentation:
Wait for command to complete, then return the
returncodeattribute.
A similar option that also waits for completion is subprocess.check_call. The difference between call and check_call is that the latter raises an exception for a nonzero return code, whereas the former returns the return code for all cases.
subprocess.check_call.From the documentation:
Run the command described by args. Wait for command to complete, then return the
returncodeattribute.
To do it asynchronously (so that you aren't waiting) you would use subprocess.Popen.
Are you trying to reproduce a shell pipeline?
If so, then, adapting the example from the python docs, your example might become:
from subprocess import Popen, PIPE
p1 = Popen([script1, input1], stdout=PIPE)
p2 = Popen([script2], stdin=p1.stdout, stdout=PIPE)
p1.stdout.close() # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]
