Issue #28383: __hash__ documentation recommends naive XOR to combine but this
is suboptimal. Update the doc to suggest to reuse the hash() method using a
tuple, with an example.
Handling zero-argument super() in __init_subclass__ and
__set_name__ involved moving __class__ initialisation to
type.__new__. This requires cooperation from custom
metaclasses to ensure that the new __classcell__ entry
is passed along appropriately.
The initial implementation of that change resulted in abruptly
broken zero-argument super() support in metaclasses that didn't
adhere to the new requirements (such as Django's metaclass for
Model definitions).
The updated approach adopted here instead emits a deprecation
warning for those cases, and makes them work the same way they
did in Python 3.5.
This patch also improves the related class machinery documentation
to cover these details and to include more reader-friendly
cross-references and index entries.
- Issue #25958: Support "anti-registration" of special methods from
various ABCs, like __hash__, __iter__ or __len__. All these (and
several more) can be set to None in an implementation class and the
behavior will be as if the method is not defined at all.
(Previously, this mechanism existed only for __hash__, to make
mutable classes unhashable.) Code contributed by Andrew Barnert and
Ivan Levkivskyi.
