On 1 December 2017 at 01:23, Ronald Oussoren <ronaldoussoren@mac.com> wrote:
1) Last time around Mark Shannon worried that this introduces infinite recursion in the language itself (in my crummy summary, please read this message to get the real concern <https://mail.python.org/pipermail/python-dev/2015-July/140938.html>). Is this truly a problem? I don’t think there is a problem, but I’m worried that I don’t fully understand Mark’s concerns.
2) PEP 487 introduced __init_subclass__ as a class method to avoid having to write a metaclass for a number of use cases. My PEP currently does require a metaclass, but it might be nicer to switch to a regular class method instead (like __init_subclass__).
I think the second point there may actually allow you to resolve the first one, by way of making `__getdescriptor__` an optional override of the typical lookup algorithm. That is: def _PyType_Lookup(tp, name): # New optional override for descriptor lookups try: # Ordinary attribute lookup, *NOT* a descriptor lookup getdesc = tp.__getdescriptor__ except AttributeError: pass else: return getdesc(name) # Default algorithm used in the absence of an override mro = tp.mro() assert isinstance(mro, tuple) for base in mro: assert isinstance(base, type) try: return base.__dict__[name] except KeyError: pass return None If you did go this way, then we'd want to add a "types.getdescriptor(cls, name)" API to expose _PyType_Lookup at the Python layer, since "getattr(type(obj), name)" wouldn't be an accurate emulation of the algorithm any more. Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia