sys.exit
exit([arg])
Exit from Python. This is implemented by raising the SystemExit exception, so cleanup actions specified by finally clauses of try statements are honored, and it is possible to intercept the exit attempt at an outer level.
The optional argument arg can be an integer
giving the exit status (defaulting to zero), or another type of
object. If it is an integer, zero is considered successful
termination
and any nonzero value is considered abnormal
termination
by shells and the like. Most systems require it to be in
the range 0-127, and produce undefined results otherwise. Some systems
have a convention for assigning specific meanings to specific exit
codes, but these are generally underdeveloped; Unix programs generally
use 2 for command line syntax errors and 1 for all other kind of
errors.
If another type of object is passed, None is equivalent to passing zero, and any other object is printed to sys.stderr and results in an exit code of 1. In particular, `sys.exit(“some error message”)` is a quick way to exit a program when an error occurs.

Comment:
What happens if you do not use sys.exit? Will python set a default status code of 0?
Posted by Daniel (2007-02-24)