Question

I am calling an external program within Python script using subprocess. The external program produces a lot of output. I need to capture the output of this program. The current code is something like this:

process = subprocess.Popen('cmd.exe', shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=None)
process.stdin.write('gams "indus89.gms"\r\n')
while process.poll() != None:
    line = process.stdout.readline()
    print line

The error I am getting with this code is

The process tried to write to a nonexistent pipe.

If I use the following code:

process = subprocess.Popen('cmd.exe', shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=None)
process.stdin.write('gams "indus89.gms"\r\n')
o, e = process.communicate()
print o 

then the output of the program is not captured.

How should I alter my code so that I can capture the output of the third party program while it runs?

Answer 1

Popen is overkill.

Try:

output = subprocess.check_output('gams "indus89.gms"\r\n', shell=True)

Hopefully that will work in your environment.