Run external program and check output and errors

import subprocess

command = ['ls', '-a']
print ' '.join(command)

try:
    print subprocess.check_output(command, stderr=subprocess.STDOUT)
except subprocess.CalledProcessError as e:
    print 'There was an error when running the command:'
    print e.output

This runs an external program an gets its output and errors.
subprocess.check_output(*popenargs, **kwargs)