Home Original page

How to get return values of a forked process

Ian Kelly ian.g.kelly at gmail.com
Tue Jun 21 14:54:57 EDT 2011 
On Tue, Jun 21, 2011 at 12:26 PM, Ian <ian.lake at rocketmail.com> wrote:
> myForkedScript has code like this:
> if fail:
>    os._exit(1)
> else:
>    os._exit(os.EX_OK)
>
> Is using os._exit() the correct way to get a return value back to the
> main process?

sys.exit() is the preferred way.

> I thought the value 'n', passed in os._exit(n) would be the value I
> get returned.  In the case of a failure, I get 256 returned rather
> than 1.

According to the docs, on Unix:

"""
Wait for completion of a child process, and return a tuple containing
its pid and exit status indication: a 16-bit number, whose low byte is
the signal number that killed the process, and whose high byte is the
exit status (if the signal number is zero); the high bit of the low
byte is set if a core file was produced.
"""

And on Windows:

"""
Wait for completion of a process given by process handle pid, and
return a tuple containing pid, and its exit status shifted left by 8
bits (shifting makes cross-platform use of the function easier).
"""

(256 >> 8) == 1

However, I would advise using the subprocess module for this instead
of the os module (which is just low-level wrappers around system
calls).
More information about the Python-list mailing list