byte types

[Gribouillis]

i suspect it is from python having the weakness of being unable to allow "user code" supporting dynamic typing the same way python itself can do

What does it mean? I don't see where Python is unable to support dynamic typing. By the way, using a generic function, you can implement a clen() function that behaves exactly the way len() does including using a __clen__() attribute for user defined types. I would implement it but I still don't understand the result that you expect from a call to clen(). Also note that officially, we should not implement new dunder methods by ourselves, just in case the python devs decide to have a __clen__ attribute someday in the future.