0 and 1 are the exit codes.
exit(0) means a clean exit without any errors / problems
exit(1) means there was some issue / error / problem and that is why the program is exiting.
This is not Python specific and is pretty common. A non-zero exit code is treated as an abnormal exit, and at times, the error code indicates what the problem was. A zero error code means a successful exit.
This is useful for other programs, shell, caller etc. to know what happened with your program and proceed accordingly.
For the record, you can use POSIX standard exit codes defined here.
import sys, os try: config() except: sys.exit(os.EX_CONFIG) try: do_stuff() except: sys.exit(os.EX_SOFTWARE) sys.exit(os.EX_OK) # code 0, all ok