Can I change the behaviour of "raise" or "Exception"?

Question

My project's code is full of blocks like the following:

try:
    execute_some_code()
except Exception:
    print(datetime.datetime.now())
    raise

simply because, if I get an error message, I'd like to know when it happened. I find it rather silly to repeat this code over and over, and I'd like to factor it away.

I don't want to decorate execute_some_code with something that does the error capturing (because sometimes it's just a block of code rather than a function call, and sometimes I don't need the exact same function to be decorated like that). I also don't want to divert stdout to some different stream that logs everything, because that would affect every other thing that gets sent to stdout as well.

Ideally, I'd like to over-ride the behaviour of either the raise statement (to also print datetime.datetime.now() on every execution) or the Exception class, to pre-pend all of its messages with the time. I can easily sub-class from Exception, but then I'd have to make sure my functions raise an instance of this subclass, and I'd have just as much code duplication as currently.

Is either of these options possible?

Answer 1

You might be able to modify python (I'd have to read code to be sure how complex that'd be), but:

You do not want to replace raise with different behaviour - trying and catching is a very pythonic approach to problem solving, so there's lots of code that works very well by e.g. calling a method and letting that method raise an exception, catching that under normal circumstances. So we can rule that approach out – you really only want to know about the exceptions you care about, not the ones that are normal during operation.

The same goes for triggering some action whenever an Exception instance is created – but:

You might be able to overwrite the global namespace; at least for things that get initialized after you declared your own Exception class. You could then add a message property that includes a timestamp. Don't do that, though – there might be people actually relying on the message to automatically react to Exceptions (bad style, but still not really seldom, sadly).