I think you need to specify the types for Mapping and MutableMapping. Maybe mypy doesn't complain with the current settings but it definitely would in strict mode.
Are you sure? I tested with strict mode and it didn't complain, also MutableMapping inherits from Mapping, regardless, we shouldn't limit this to MutableMapping only.
Are you sure? I tested with strict mode and it didn't complain, also MutableMapping inherits from Mapping, regardless, we shouldn't limit this to MutableMapping only.