bpo-42064: Move sqlite3 exceptions to global state, part 1 of 2

[erlend-aasland]

Also adds a test to verify the (borrowed) exceptions in sqlite3.Connection.

https://bugs.python.org/issue42064

Automerge-Triggered-By: GH:encukou

[erlend-aasland]

@encukou Whenever you have time, would you mind reviewing this as well? I've split this operation in two; moving all exceptions was too large a diff.

[encukou]

Looks OK at first glance but I'll do a review next week (after 3.10 beta 3)

[erlend-aasland]

I just remembered that all the connection object keeps borrowed references to all the sqlite3 exception types; we should use that instead of the module state where possible. See 4fe9d98.

[encukou]

I just remembered that all the connection object keeps borrowed references to all the sqlite3 exception types

I see the connection type is created with PyType_FromModuleAndSpec, so connections hold a reference to the module through their type. (So the module is kept alive and the connections can borrow from it safely).
But, borrowed references tend to be confusing – you always have to think about things like this, even in the future as changes made in seemingly unrelated parts.
Is it worth it to update them to strong references? Or just one strong reference to the module?

[encukou]

The changes themselves look OK!

[erlend-aasland]

But, borrowed references tend to be confusing – you always have to think about things like this, even in the future as changes made in seemingly unrelated parts.
Is it worth it to update them to strong references? Or just one strong reference to the module?

Yes, I've thought about this. I think updating them to strong references is a good idea.

[erlend-aasland]

Thanks for reviewing, Petr!