python - os.exec on Windows

Question

I have a script that calls os.execvp into another Python instance. After doing this, I appear to be attached to a cmd.exe instance, not the Python instance I just created. The Python instance responds to Ctrl+C however.

H:\bin>Python 3.2.1 (default, Jul 10 2011, 21:51:15) [MSC v.1500
 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print('hi')
Can't find file ('hi')

H:\bin>

H:\bin>
KeyboardInterrupt
>>> echo hi
hi

The call to exec:

from sys import argv
os.execvp('python', argv)

How do I replace the original Python instance with the new one, as per the behaviour one might see on Linux?

Related: bugs.python.org/issue9148. According to Amaury Forgeot d'Arc's comment - on Windows, exec() does not really replace the current process. It creates a new process (with a new pid), and exits the current one. Hence the calling program only sees that the script has terminated. I don't see any easy solution on Windows, except than using subprocess.Popen(), and exit the script when the subprocess terminates. Does it look like a possible solution in your case? — Piotr Dobrogost
Thanks for the useful comment @PiotrDobrogost. If you related the material in the Python issue to this question that would constitute a solution. — Matt Joiner
You mean like first calling subprocess.Popen() and then exiting from the original Python process? — Piotr Dobrogost
@PiotrDobrogost: Yes, in the interest of people following this same problem, they deserve a clean solution and justification. — Matt Joiner
@MattJoiner Hi, I just stumbled into this while trying to port a library to Windows. I am struggling to find a complete, working example based on subprocess.Popen. Any idea where I could find one? — s-m-e

Zart Zart · Accepted Answer · 2011-08-12T06:54:09

On Unix executing binaries is split into two stages - fork(3) to clone current process and exec(3) to load executable into address space. On windows there is only CreateProcess which does the same thing as fork+exec.

For portability your best bet is to use subprocess.Popen (which also does proper filename quoting on Windows unlike os.* counterparts) as in http://docs.python.org/library/subprocess.html#replacing-the-os-spawn-family

python - os.exec on Windows

1 Answers