On Wed, Mar 31, 2021 at 2:30 AM Mark Shannon <m...@hotpy.org> wrote: > > - Add new `__match_seq__` and `__match_map__` special attributes, > corresponding to new public `Py_TPFLAGS_MATCH_SEQ` and > `Py_TPFLAGS_MATCH_MAP` flags for use in `tp_flags`. When Python classes are > defined with one or both of these attributes set to a boolean value, > `type.__new__` will update the flags on the type to reflect the change > (using a similar mechanism as `__slots__` definitions). They will be > inherited otherwise. For convenience, `collections.abc.Sequence` will > define `__match_seq__ = True`, and `collections.abc.Mapping` will define > `__match_map__ = True`. > > > > Using this in Python would look like: > > > > ``` > > class MySeq: > > __match_seq__ = True > > ... > > > > class MyMap: > > __match_map__ = True > > ... > > ``` > > I don't like the way this need special inheritance rules, where > inheriting one attribute mutates the value of another. > It seems convoluted. > > Consider: > > class WhatIsIt(MySeq, MyMap): > pass > > With __match_container__ it works as expected with no special > inheritance rules. >
Wait a minute, do you expect WhatIsIt to be a sequence but not a map? *I* would expect that it is both, and that's exactly what Brandt's proposal does. So I see this as a plus. > I think we are close to agreement on the mechanism for selecting which > pattern to match, but I still want the better defined semantics of PEP 653. > I don't know that PEP 653's semantics are better. Have you analyzed any *differences* besides the proposal above? I've personally found reading your pseudo-code very difficult, so I simply don't know. -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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