I write a server which handles events and uncaught exceptions during handling the event must not terminate the server.
The server is a single non-threaded python process.
I want to terminate on these errors types:
The list of built in exceptions is long: https://docs.python.org/2/library/exceptions.html
I don't want to re-invent this exception handling, since I guess it was done several times before.
How to proceed?
Hint: This question is not about running a unix daemon in background. It is not about double fork and not about redirecting stdin/stdout :-)
The top-most exception is BaseException
. There are two groups under that:
Exception
derivedThings like Stopiteration
, ValueError
, TypeError
, etc., are all examples of Exception
.
Things like GeneratorExit
, SystemExit
and KeyboardInterrupt
are not descended from Execption
.
So the first step is to catch Exception
and not BaseException
which will allow you to easily terminate the program. I recommend also catching GeneratorExit
as 1) it should never actually be seen unless it is raised manually; 2) you can log it and restart the loop; and 3) it is intended to signal a generator has exited and can be cleaned up, not that the program should exit.
The next step is to log each exception with enough detail that you have the possibility of figuring out what went wrong (when you later get around to debugging).
Finally, you have to decide for yourself which, if any, of the Exception
derived exceptions you want to terminate on: I would suggest RuntimeError
and MemoryError
, although you may be able to get around those by simply stopping and restarting your server loop.
So, really, it's up to you.
If there is some other error (such as IOError
when trying to load a config file) that is serious enough to quit on, then the code responsible for loading the config file should be smart enough to catch that IOError
and raise SystemExit
instead.
As far as whitelist/blacklist -- use a black list, as there should only be a handful, if any, Exception
-based exceptions that you need to actually terminate the server on.