Capture stdin output from popen2

[maddog39]

Hello all,

In my python application I am trying to capture the output of stdin from a command that I run via popen2(). The python docs say that it returns a tuple of (stdin, stdout) however and i run:

result = popen2(command)[0].read()

It only prints the results to the console and never returns a result to the variable. Whats going on?

Thanks!
-Alec Hussey

[Duoas]

It sounds to me like your child process is misbehaving. May I ask which command you are executing?

[maddog39]

Im executing gcc to compile a file in this instance.

[Duoas]

On linux? Or windows?

[jrcagle]

Well, first off there are two versions of popen2(). One is os.popen2(command), and it returns (child_stdin, child_stdout).

The other is popen2.popen2(command), and perversely, it returns (child_stdout, child_stdin).

So make sure that you don't have the two reversed.

(Who made that decision, anyways?! Grr...)

Jeff

[maddog39]

I am on linux, and I am using the popen2 module.
http://docs.python.org/lib/module-popen2.html

[Edit]
Thats my mistake then isn't it? I am reading from the first element of the tuple, when I should be reading from the second one.

[Duoas]

No, you had that correct. The return tuple is (child's output, child's input).

I don't know what's wrong...

[EDIT]
I just had a thought. Is your C program compiling correctly or is it producing errors? You might have to use popen3()...

[maddog39]

Yea, aaah. I intentionally put syntax errors in there to test it. But gcc is most likely printing those errors to stderr and thats why its not capturing them. Alright, I'll try it with popen3.

[Edit]
Actually, popen4() would probably work better, but whatever works I guess.

[Edit]
Now it works! Thanks alot!