Directing script output to a file using subprocess?

Question

From within a python script ("main.py"), I am using the subprocess module to run another script ("sub_script.py").

Here's the code in the "main.py" script that 'runs' "sub_script.py":

subprocess.Popen([sys.executable, "sub_script.py"])

this works fine as long as "sub_script.py" does not have any "print" statements in it.

I now want to channel all the output of "sub_script.py" to an external file ("log.txt").

How do I do it?

Why not just import sub_script? Why all this extra subprocess business? — S.Lott
– S.Lott, Commented Dec 20, 2010 at 19:26
I am running "main.py" using Cron -- so it is helpful for me to use subprocess. — user3262424
– user3262424, Commented Dec 20, 2010 at 19:40
import and launching a subprocess do fundamentally different things. For starters, the script won't run with import at all if it uses if __name__ = "__main__": block, you'd have trouble forwarding the output (which is required here), and your main script would need to wait for the subscript to finish. Also you can't really import a script in the general case (because you don't have any guarantee that it is a .py file in the python path). — Rosh Oxymoron
– Rosh Oxymoron, Commented Dec 20, 2010 at 19:43
@user540009: "so it is helpful for me to use subprocess"? Why? Please explain why. @Rosh Oxymoron: Using import sub_script is not the entire line of code required, more would be needed, clearly. "Forwarding the output" from the original script and the original script which imports and executes sub_script.py does not change. I'm not sure what "import a script in the general case" means since importing a script requires some design work, i.e., setting PYTHONPATH. The question remains. Why not simply import and execute sub_script? Why try to use subprocess? — S.Lott
– S.Lott, Commented Dec 20, 2010 at 20:32

Rosh Oxymoron · Accepted Answer · 2010-12-20 19:37:41Z

2

subprocess.Popen([sys.executable, "sub_script.py"], stdout=open("log.txt", "a"))

answered Dec 20, 2010 at 19:37

Rosh Oxymoron

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