store subprocess popen in variable code example

Example 1: python subprocess exception handling

try:
    subprocess.check_output(...)
except subprocess.CalledProcessError as e:
    print(e.output)

Example 2: python write subprocess stdout stderr to file

with open("stdout.txt","wb") as out, open("stderr.txt","wb") as err:
    subprocess.Popen("ls",stdout=out,stderr=err)