I think you're looking for something more like the multiprocessing module:
http://docs.python.org/library/multiprocessing.html#the-process-class
The subprocess module is for spawning processes and doing things with their input/output - not for running functions.
Here is a multiprocessing version of your code:
from multiprocessing import Process, Queue
# must be a global function
def my_function(q, x):
q.put(x + 100)
if __name__ == '__main__':
queue = Queue()
p = Process(target=my_function, args=(queue, 1))
p.start()
p.join() # this blocks until the process terminates
result = queue.get()
print result
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I think you're looking for something more like the multiprocessing module:
http://docs.python.org/library/multiprocessing.html#the-process-class
The subprocess module is for spawning processes and doing things with their input/output - not for running functions.
Here is a multiprocessing version of your code:
from multiprocessing import Process, Queue
# must be a global function
def my_function(q, x):
q.put(x + 100)
if __name__ == '__main__':
queue = Queue()
p = Process(target=my_function, args=(queue, 1))
p.start()
p.join() # this blocks until the process terminates
result = queue.get()
print result
You can use the standard Unix fork system call, as os.fork(). fork() will create a new process, with the same script running. In the new process, it will return 0, while in the old process it will return the process ID of the new process.
child_pid = os.fork()
if child_pid == 0:
print "New proc"
else:
print "Old proc"
For a higher level library, that provides multiprocessing support that provides a portable abstraction for using multiple processes, there's the multiprocessing module. There's an article on IBM DeveloperWorks, Multiprocessing with Python, with a brief introduction to both techniques.
The stack trace suggests you're using Windows as the operating system. ls not something that you will typically find on a Windows machine unless using something like CygWin.
Instead, try one of these options:
# use python's standard library function instead of invoking a subprocess
import os
os.listdir()
# invoke cmd and call the `dir` command
import subprocess
subprocess.run(["cmd", "/c", "dir"])
# invoke PowerShell and call the `ls` command, which is actually an alias for `Get-ChildItem`
import subprocess
subprocess.run(["powershell", "-c", "ls"])
ls is not a Windows command. The windows analogue is dir, so you could do something like
import subprocess
subprocess.run(['cmd', '/c', 'dir'])
However, if you're really just trying to list a directory it would be much better (and portable) to use something like os.listdir()
import os
os.listdir()
or pathlib
from pathlib import Path
list(Path().iterdir())
If 'somescript.py' isn't something you could normally execute directly from the command line (I.e., $: somescript.py works), then you can't call it directly using call.
Remember that the way Popen works is that the first argument is the program that it executes, and the rest are the arguments passed to that program. In this case, the program is actually python, not your script. So the following will work as you expect:
subprocess.call(['python', 'somescript.py', somescript_arg1, somescript_val1,...])
This correctly calls the Python interpreter and tells it to execute your script with the given arguments.
Note that this is different from the above suggestion:
subprocess.call(['python somescript.py'])
That will try to execute the program called python somscript.py, which clearly doesn't exist.
call('python somescript.py', shell=True)
Will also work, but using strings as input to call is not cross platform, is dangerous if you aren't the one building the string, and should generally be avoided if at all possible.
Windows? Unix?
Unix will need a shebang and exec attribute to work:
#!/usr/bin/env python
as the first line of script and:
chmod u+x script.py
at command-line or
call('python script.py'.split())
as mentioned previously.
Windows should work if you add the shell=True parameter to the "call" call.