Inheritance for native types is not supported
Default load_attr implementation (as used for all native types) doesn't take type inheritance (->bases_tuple) into account. I'm working on OrderedDict implementation, and it inherits most of its methods from dict, but adds few (well, 1) new method. Of course, this new method can be ignored, and old trick of putting the same .locals_dict to both types can be used. But I wanted to look into making truly inheritable methods, which requires setting custom .load_attr type method. And we already have implementation of this method which takes inheritance into account - for user classes/instances. But trying to use it, it assumes that object whose attr is being looked up is instance, so making it work with native objects means adding even more conditions to existing bunch of those (and which are already pretty mind-boggling). Another alternative is to make clean, "optimized" inheritance-friendly .load_attr for native types, but that means code duplication (and refactoring of existing code paths, factoring out functions, which means more stack usage, etc.)
Any thoughts?
py/runtime: Do generic lookup if type->attr fails.
If the custom type->attr fails, don't give up just yet but look in the
locals_dict. This allows type->attr to extend rather than completely
replace the lookup.
This is useful for custom builtin classes that have mostly regular
methods but just a few special attributes/properties. This way,
type->attr needs to deal with the special cases only and the default
lookup will be used for generic methods.
This is an alternative to https://github.com/micropython/micropython/pull/4969.
The original was perhaps slightly more convenient since no custom
attr handler was required, but this is a much smaller change overall.
This new PR is also a bit more generic, as this makes it quite easy to add
properties that do a bit more than just returning an existing attribute.
EDIT: Rebased onto latest master.