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up vote 1 down vote favorite

I have a python script that needs to invoke another python script in the same directory. I did this:

    from subprocess import call
    call('somescript.py')

I get the following error 

    call('somescript.py')
    File "/usr/lib/python2.6/subprocess.py", line 480, in call
    return Popen(*popenargs, **kwargs).wait()
    File "/usr/lib/python2.6/subprocess.py", line 633, in __init__
    errread, errwrite)
    File "/usr/lib/python2.6/subprocess.py", line 1139, in _execute_child
raise child_exception

OSError: [Errno 2] No such file or directory

I have the script somescript.py in the same folder though. Am i missing something here. Thanks

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1  
Is . in your PATH? Is somescript.py executable? –  Wooble Aug 22 '11 at 19:17
    
Why are you trying to execute it? why not import it? –  tMC Aug 22 '11 at 20:10
    
@wooble yes. It is in path and and executable too. Yes. I could also import it. But would eitherway like to know what i am doing wrong here since i think this is supposed to work. –  user514946 Aug 22 '11 at 22:04

7 Answers 7

up vote 2 down vote

if you're on Linux/Unix you could avoid call() altogether and not execute an entirely new instance of the Python executable and its environment.

import os

cpid = os.fork()
if not cpid:
    import somescript
    os._exit(0)

os.waitpid(cpid, 0)

FWIW

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Only *nix: using fork you will inherit from the parent process python interpreter (with all existing imports, ...). If you want a brand new interpretor this not a good choice. See the diff fork/exec unix system call. –  Nicolae Dascalu Aug 23 '11 at 2:46
    
subprocess module uses fork/exec on POSIX systems and CreateProcess on Windows. No need to use fork directly if you want to run a Python script. –  J.F. Sebastian Apr 5 at 11:35
up vote 2 down vote

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.

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1  
call('python script.py') won't work on non-Windows systems. It should be check_call([sys.executable or 'python', '/path/to/script.py']). And you don't need the shebang and executable permissions if python executable is specified. –  J.F. Sebastian Apr 5 at 11:30
up vote 1 down vote

subprocess.call expects the same arguments as subprocess.Popen - that is a list of strings (the argv in c) rather then a single string. It's quite possible that your child process attempted to run "s" with the parameters "o", "m", "e"...

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oh yeah, good point too about the list of strings...forgot about that. –  jsh Aug 22 '11 at 19:21
up vote 0 down vote

subprocess call is a very literal-minded system call. it can be used for any generic process...hence does not know what to do with a python script automatically.

try 

call ('python somescript.py')

if that doesn't work, you might want to try an absolute path, and/or check permissions on your python script...the typical fun stuff.

j

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up vote 0 down vote

First, check if somescript.py is executable and starts with something along the lines of #!/usr/bin/python. If this is done, then you can use subprocess.call('./somescript.py').

Or as another answer points out, you could do subprocess.call(['python', 'somescript.py']).

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Just a random pointer: I've found it to be useful to use #!/usr/bin/env python so that if a module has been loaded, you are automatically running with the loaded python version. –  Vorticity Aug 22 '11 at 21:56
up vote 0 down vote

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.

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up vote 0 down vote 
def main(argv):
    host = argv[0]
    type = argv[1]
    val = argv[2]

    ping = subprocess.Popen(['python ftp.py %s %s %s'%(host,type,val)],stdout = subprocess.PIPE,stderr = subprocess.PIPE,shell=True)
    out = ping.communicate()[0]
    output = str(out)
    print output
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