+1. I also don’t see what’s the big deal. On Wed, Mar 31, 2021 at 19:27 Caleb Donovick <donov...@cs.stanford.edu> wrote:
> > It's a stronger statement than simply undoing > > the declaration that it's a sequence. There would be no way to reset > > to the default state. > > How is this different from anything else that is inherited? > > The setting of a flag to `False` is not some irreversible process which > permanently blocks child classes from setting that flag to `True`. > If I want to give priority to `Seq` over `Parent` in Brandt's original > example I need only switch the order of inheritance so that `Seq` is > earlier in `Child` MRO or explicitly set the flag to `True` (or > `Seq.__match_seq__`). In contrast Brandt's scheme does irreversibly > set flags, there is no way to undo the setting of `__match_seq__` in a > parent class. > > This really doesn't seem like an issue to me. I can't personally think of > a use case for explicitly setting a flag to `False` > but I also don't see why it should be forbidden. We get "- Otherwise, set > the flag if any of the parents set have the flag set" > for free through normal MRO rules except in the case where there is an > explicit `False` (which I assume will be exceedingly rare > and if it isn't there is clearly some use case). Why make it more > complicated? > > On Wed, Mar 31, 2021 at 6:05 PM Chris Angelico <ros...@gmail.com> wrote: > >> On Thu, Apr 1, 2021 at 11:54 AM Caleb Donovick <donov...@cs.stanford.edu> >> wrote: >> > >> > > Here, `Child` will *not* match as a sequence, even though it probably >> should, >> > >> > Strong disagree, if I explicitly set `__match_seq__` to `False` in >> `Parent` I probably have a good reason for it and would absolutely expect >> `Child` to not match as a sequence. >> > >> >> How much difference is there between: >> >> class Grandparent: >> """Not a sequence""" >> class Parent(Grandparent): >> """Also not a sequence""" >> class Child(Parent): >> """No sequences here""" >> >> and this: >> >> class Grandparent(list): >> """Is a sequence""" >> class Parent(Grandparent): >> """Explicitly not a sequence""" >> __match_seq__ = False >> class Child(Parent): >> """Shouldn't be a sequence""" >> >> >> ? Either way, Parent should function as a non-sequence. But if Child >> inherits from both Parent and tuple, it is most definitely a tuple, >> and therefore should be a sequence. >> >> With your proposed semantics, setting __match_seq__ to False is not >> simply saying "this isn't a sequence", but it's saying "prevent this >> from being a sequence". It's a stronger statement than simply undoing >> the declaration that it's a sequence. There would be no way to reset >> to the default state. >> >> Brandt's proposed semantics sound complicated, but as far as I can >> tell, they give sane results in all cases. >> >> ChrisA >> _______________________________________________ >> Python-Dev mailing list -- python-dev@python.org >> To unsubscribe send an email to python-dev-le...@python.org >> https://mail.python.org/mailman3/lists/python-dev.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-dev@python.org/message/GKOUSL2CPMO7NPPTK2E7XE7LXTPDVRDJ/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/UWSPAA27Q2ZE44YHK7ZKQCO5YZ2HG32F/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido (mobile)
_______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/LVVS7YUUC37OZQLHDQZXKSEZ2GNQCSXB/ Code of Conduct: http://python.org/psf/codeofconduct/
