Question

in the following for loop, i print the version number of program installed

 for program in sub3_required_programs:
        try:
            version = subprocess.call([program, '-i'])                                                                     
            print version + '\n'
        except:
            exit

But i actually want only the first line which has the version number. How can i restrict the print to only the first line

Answer 1

What’s the current print output? Unless you’re running a version of Python that behaves differently, it looks like the return status of the call is the only thing being assigned to version.

Run command with arguments. Wait for command to complete, then return
the returncode attribute.

– docstring for subprocess.call

I bet the subprocess.call is the culprit, printing it’s output to STDOUT. Even if you didn’t have that print statement, you would still see all the output of the subprocess call due to the way the method works.

To grab the actual output, you might want to do something more like

lines = subprocess.Popen([program, '-i'], stdout=subprocess.PIPE).communicate()[0]
print lines.splitlines()[0] + '\n'

The communicate call returns the tuple (stdoutdata, stderrdata). You can read more about it in the docs. Everything else should be self-explanatory.