Discussion: what exception to raise for a failed lookup by id?

[elliot-100]

Currently get_event(id) and get_group(id) raise built-in IndexError if id is not matched. NB IndexError subclasses base class LookupError.

Although I originally implemented this, I don't think it's correct, as (paraphasing docs) this is intended where an integer subscript is out of range; and id is str not int.

@ptmminh suggested ValueError (docs) but this should be:

raised when an operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception such as IndexError.

I think we should be more precise, and so it should be one of:

• built-in KeyError (docs) which subclasses base class LookupError - as id is a key to a mapping (dict), even though it happens to be inside a list
• custom exception e.g. IDMatchError which subclasses base class LookupError

Let me know what you think.

[dhomeier]

Would have considered ValueError as well, but as the docs state a more precise exception type should be preferred, I'd agree with •1 that KeyError would be that more precise type, and also what I'd generally expect in such a case.

[ptmminh]

sorry @elliot-100 I missed this note earlier! Agree that KeyError is probably best!