Matthias Görgens wrote:
If the target of the call isn't in an appropriate state, isn't that a bug in the constructor that it allows you to construct objects that are in an invalid state? You should fix the object so that it is never in an invalid state rather than blaming the caller. You can't really do that with files that have been closed. Unless you disallow manual closing of files altogether. That being said, I'd suggest that people raise custom exception, so your callers can catch exactly what they want to handle. An generic exception like ValueError or the proposed InvalidStateError could be thrown by almost anything you call in your block, instead of just what you actually intend to catch.
It depends on context whether it makes sense to define a custom exception, and I agree that I frequently should define a custom exception. In that case though, it would still be nice to have an appropriate generic exception for that to inherit from, just as I would inherit from `ValueError` for a special case of a value error.