[Python-ideas] Exception for developer errors?

Elazar elazarg at gmail.com
Wed Apr 10 18:13:50 EDT 2019

You have AssertionError for that.


בתאריך יום ה׳, 11 באפר׳ 2019, 1:10, מאת Stefano Borini ‏<
stefano.borini at gmail.com>:

> I occasionally found situations where I want to raise an exception for
> errors that can only arise because the developer made a mistake, for
> example:
> - an abstract method is supposed to be reimplemented and its execution
> is supposed to leave some internal constraints of an object unchanged,
> but these are instead violated.
> - an impossible "else" condition after an if/elif, where the else
> cannot simply happen unless someone really screwed up the internal
> state of the object.
> In general, when these cases happen, I use RuntimeError, but other
> people may choose otherwise. I've also seen ValueError, plain
> Exception or a specifically made subclass used in these cases.
> Whatever the choice is, it generally lacks clarity of communication to
> whoever receives it.
> RuntimeError is a rather generic exception according to the
> documentation, and you can only rely on the message, which relies on
> writing something appropriate for the situation:
> ```
> exception RuntimeError
> Raised when an error is detected that doesn’t fall in any of the other
> categories. The associated value is a string indicating what precisely
> went wrong.
> ```
> while it would be useful to communicate clearly to whoever is using or
> modifying the code "listen, it's your mistake, you misunderstood how I
> work or you ruined my internals, leading me to an impossible state".
> Also, customers seeing this kind of exception would understand without
> a doubt that the application is broken because of an internal error.
> I tried some search on the mailing list but could not find anything at
> a glance about this topic. Was this already discussed in the past?
> Thanks
> --
> Kind regards,
> Stefano Borini
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