Hi Eric, A few quick comments:
Why do you even have a hash= argument on individual fields? For the whole class, I can imagine you might want to explicitly mark a whole class as unhashable, but it seems like the only thing you can do with the field-level hash= argument is to create a class where the __hash__ and __eq__ take different fields into account, and why would you ever want that? Though honestly I can see a reasonable argument for removing the class-level hash= option too. And even if you keep it you might want to error on some truly nonsensical options like defining __hash__ without __eq__. (Also watch out that Python's usual rule about defining __eq__ blocking the inheritance of __hash__ does not kick in if __eq__ is added after the class is created.) I've sometimes wished that attrs let me control whether it generated equality methods (eq/ne/hash) separately from ordering methods (lt/gt/...). Maybe the cmp= argument should take an enum with options none/equality-only/full? The "why not attrs" section kind of reads like "because it's too popular and useful"? -n On Sep 8, 2017 08:44, "Eric V. Smith" <e...@trueblade.com> wrote: Oops, I forgot the link. It should show up shortly at https://www.python.org/dev/peps/pep-0557/. Eric. On 9/8/17 7:57 AM, Eric V. Smith wrote: > I've written a PEP for what might be thought of as "mutable namedtuples > with defaults, but not inheriting tuple's behavior" (a mouthful, but it > sounded simpler when I first thought of it). It's heavily influenced by > the attrs project. It uses PEP 526 type annotations to define fields. > From the overview section: > > @dataclass > class InventoryItem: > name: str > unit_price: float > quantity_on_hand: int = 0 > > def total_cost(self) -> float: > return self.unit_price * self.quantity_on_hand > > Will automatically add these methods: > > def __init__(self, name: str, unit_price: float, quantity_on_hand: int > = 0) -> None: > self.name = name > self.unit_price = unit_price > self.quantity_on_hand = quantity_on_hand > def __repr__(self): > return > f'InventoryItem(name={self.name!r},unit_price={self.unit_pri > ce!r},quantity_on_hand={self.quantity_on_hand!r})' > > def __eq__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) == > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > def __ne__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) != > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > def __lt__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) < > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > def __le__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) <= > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > def __gt__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) > > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > def __ge__(self, other): > if other.__class__ is self.__class__: > return (self.name, self.unit_price, self.quantity_on_hand) >= > (other.name, other.unit_price, other.quantity_on_hand) > return NotImplemented > > Data Classes saves you from writing and maintaining these functions. > > The PEP is largely complete, but could use some filling out in places. > Comments welcome! > > Eric. > > P.S. I wrote this PEP when I was in my happy place. > > _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/njs% 40pobox.com
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