Question

I am attempting to run a command in terminal through a Python script. The command, which only takes three arguments, works perfectly when performed in terminal. Here is what is entered in the command line:

gpmetis inputfile numberOfSections

Wherever the inputfile is from, say the Desktop, the outputfile is dumped in the same location after gpmetis is executed (it is named inputfile.part.numberOfSections). gpmetis only works in terminal, but for condensing purposes, I want to use it during the middle of the Python script to save time. (I would previously just shuffle around files to and from terminal and Python)

But this is where I run into problems… this question and this forum gave helpful hints on how to execute terminal within Python, but I’m still not receiving the outputfile when I run the python code. It’s like the output is suppressed or the way I call terminal is faulty.

I’m currently calling terminal like:

def Terminal(inputfile, NumParts): 
    os.system("gpmetis inputfile NumParts")

    outputfile = "inputfile.part." + NumParts
    return outputfile

And I don’t get an error from this, but I don’t receive any output file either. What am I missing here and if you know could you explain it? I’m trying to learn Python, so describing what I’m screwing up would be much appreciated.

os has been imported. There may be a fault with how I am “returning” the outputfile in my script, but I also do not see an outputfile on my desktop, which is the first problem to be dealt with (one step at a time!)

NOTE: I found documentation that is related, but will it help me? I’m having trouble understanding it..

Answer 1

First, you might check the return value of os.system. A non-zero return value usually indicates that an error has occurred.

It looks like you are trying to use the parameters in your command. In that case it should look like:

def Terminal(inputfile, NumParts): 
    command = 'gpmetis ' + inputfile + ' ' + str(NumParts)
    os.system(command)

    outputfile = intputfile + '.part.' + str(NumParts)
    return outputfile

Lastly, based on this answer, it looks like you may be better off using the subprocess module. You can then execute the same command like this:

import subprocess
subprocess.call(['gpmetis', inputfile, str(NumParts)])