> Previously, the only way to add a dialect was through register_dialect that does
> type checking to make sure it gets a legit dialect object. Now, the _dialects dict is 
> directly accessible to Python code and it can add arbitrary objects to it (both as
> keys and as values). Does this mean that the C code now has to do type checking in all 
> internal code that accesses _dialects?

You are right, I forgot about that part. That will make the patch significantly more complicated.

> However, it's a step in the right direction in case we do have multiple instances of
> the extension module alive at the same time in the future. Although then it would be
> interesting to consider how to find the actually correct module instance from internal 
> functions.

This sounds basically impossible (which is why we *can't* have multiple instances of an extension module alive in a single interpreter :-)).