How to know and prevent an error with terminal commands from python?

Making a program which can open apps upon listening to commands. The app name is stored in variable 'a'. And then opened with the following line:

os.system("open /Applications/" + a + ".app")

But sometimes it is possible that 'a' does not exist on the system, say 'music' for which the console prints:

The file /Applications/music.app does not exist.

And the python code stops entirely.

How can I know that the console gave this error and prevent the program from stopping?

Solution

subprocess is more powerful than os.system, the stdout and stderr of subprocess can be ignored with subprocess

import subprocess
res=subprocess.run(["open", "/Applications/" + a + ".app"])
print(res.returncode)

use res.returncode to get the execute result(none zero value shows that the sub process has encountered errors).