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It's a bit more complicated than that. The C code you point to is for dbm.ndbm. The class at issue in this file, dbm._Database, doesn't exist at runtime. We use it as the return type for dbm.open, which can return an instance of any of the database classes in the dbm package. I think the intent is that dbm._Database reflects the common interface of all three. Maybe we should use a Union return type instead?

I think for now I'll switch it to str | bytes, which are the types that all three dbm implementations support. (dbm.dumb is str | bytes | bytearray, the other two are str | ReadOnlyBuffer).