Python 3: Get and Check Exit Status Code (Return Code) from subprocess.run()
When running a command using subprocess.run() , the exit status code of the command is available as the .returncode property in the CompletedProcess object returned by run() :
from subprocess import run p = run( [ 'echo', 'Hello, world!' ] ) print( 'exit status code:', p.returncode )
Check Exit Status Code and Raise Error if Non-Zero
Manual Check
If we want our script to stop running and raise an error if the subprocess returns a non-zero exit status code, we could manually check the returncode property of the CompletedProcess object that run() returns:
from subprocess import run print( 'Running command. ' ) p = run( [ 'cat', '/foo' ] ) if p.returncode != 0: raise Exception( f'Invalid result: < p.returncode >' ) # If `cat /foo` fails above, we won't get here. print( 'All done!' )
check=True Option (Shorter Code)
But the shorter way to accomplish the same thing is to just set check=True when we call run() :
from subprocess import run print( 'Running command. ' ) run( [ 'cat', '/foo' ], check=True ) # If `cat /foo` fails above, we won't get here. print( 'All done!' )
Assuming we don’t have a file /foo on our system, cat /foo will return a non-zero exit status code. If we run the code above on a Linux-based system, we’ll see output like this:
Running command. cat: /foo: No such file or directory Traceback (most recent call last): File "test.py", line 4, in run( [ 'cat', '/foo' ], check=True ) File "/usr/lib/python3.8/subprocess.py", line 512, in run raise CalledProcessError(retcode, process.args, subprocess.CalledProcessError: Command '['cat', '/foo']' returned non-zero exit status 1.
Note that All Done! is never printed because the script raised an error before it got to line 5.
If we omit the check=True option:
from subprocess import run print( 'Running command. ' ) run( [ 'cat', '/foo' ] ) # Even if `cat /foo` fails above, we will always get here. print( 'All done!' )
check defaults to False , so we won’t see an error message, and we will see the All done! line:
Running command. cat: /foo: No such file or directory All done!