How can I call a python script from a python script

Question

I have a python script 'b.py' which prints out time ever 5 sec.

while (1):
   print "Start : %s" % time.ctime()
   time.sleep( 5 )
   print "End : %s" % time.ctime()
   time.sleep( 5 )

And in my a.py, I call b.py by:

def run_b():
        print "Calling run b"
    try:
        cmd = ["./b.py"]

        p = subprocess.Popen(cmd,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.STDOUT)

        for line in iter(p.stdout.readline, b''):
                        print (">>>" + line.rstrip())


    except OSError as e:
        print >>sys.stderr, "fcs Execution failed:", e  

    return None

and later on, I kill 'b.py' by: PS_PATH = "/usr/bin/ps -efW"

def kill_b(program):
    try:

        cmd = shlex.split(PS_PATH)

        retval = subprocess.check_output(cmd).rstrip()
        for line in retval.splitlines():

            if program in line:
                print "line =" + line
                pid = line.split(None)[1]
                os.kill(int(pid), signal.SIGKILL)

    except OSError as e:
        print >>sys.stderr, "kill_all Execution failed:", e
    except subprocess.CalledProcessError as e:
        print >>sys.stderr, "kill_all Execution failed:", e

run_b()
time.sleep(600)
kill_b("b.py")

I have 2 questions. 1. why I don't see any prints out from 'b.py' and when I do 'ps -efW' I don't see a process named 'b.py'? 2. Why when I kill a process like above, I see 'permission declined'?

I am running above script on cygwin under windows.

Thank you.

an easier way to kill b.py is to return p from run_b() before starting to read b.py's output and call p.kill(); p.wait() later. — jfs
– jfs, Commented Aug 21, 2013 at 20:03
check that ./b.py is started successfully (p.poll() should be None) — jfs
– jfs, Commented Aug 21, 2013 at 22:54

martineau · Accepted Answer · 2017-01-21 17:52:42Z

1

Why I don't see any prints out from 'b.py' and when I do 'ps -efW' I don't see a process named 'b.py'?

Change run_b() lines:
```
p = subprocess.Popen(cmd,
                     stdout=sys.stdout,
                     stderr=sys.stderr)
```
You will not see a process named "b.py" but something like "python b.py" which is little different. You should use pid instead of name to find it (in your code "p.pid" has the pid).
Why when I kill a process like above, I see 'permission declined'?

os.kill is supported under Windows only 2.7+ and acts a little bit different than posix version. However you can use "p.pid". Best way to kill a process in a cross platform way is:
```
if platform.system() == "Windows":
    subprocess.Popen("taskkill /F /T /PID %i" % p.pid, shell=True)
else:
    os.killpg(p.pid, signal.SIGKILL)
```

killpg works also on OS X and other Unixy operating systems.

edited Jan 21, 2017 at 17:52

martineau

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answered Oct 25, 2013 at 9:08

J_Zar

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1 Comment

martineau Over a year ago

To run another Python script from the current one, cmd would need to be sys.executable and it would also need to have the script name, "./b.py", passed as a argument.

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