Python subprocess.check_output

Question

I am trying to use a couple shell level commands from Python to get and set variables for later use in my program but it does not appear to be calling the commands properly as the outputs should be simple 1-liners. Not quite sure if it's due to the % or ; signs.

current_vcodec = subprocess.check_output(["mediainfo", "--Inform='Video;%CodecID%'", "%s" % source])
current_acodec = subprocess.check_output(["mediainfo", "--Inform='Audio;%CodecID%'", "%s" % source])
duration = subprocess.check_output(["mediainfo", "--Inform='Video;%Duration%'", "%s" % source])

Answer 1

I highly recommend you use Kenneth Reitz's envoy python wrapper for subprocess. It makes calls to command line far easier to use.

import envoy
res = envoy.run("mediainfo --Inform='Video;%CodecID%' {0}".format(source))
if res.status_code != 0:
   print("media info failure: {0}".format(res.std_out + " " + res.std_err))
 else:
   print(res.std_out)
   current_vcodec = res.std_out

If you needed, you can "escape" the % with a backslash, but I'm not sure that's the problem. The ; shouldn't be a problem.

Answer 2

Ok, I got it working. This is the syntax that gave the correct output.

current_vcodec = subprocess.check_output("mediainfo --Inform='Video;%%CodecID%%' %s" % source, shell=True)
current_acodec = subprocess.check_output("mediainfo --Inform='Audio;%%CodecID%%' %s" % source, shell=True)
duration = subprocess.check_output("mediainfo --Inform='Video;%%Duration%%' %s" % source, shell=True)