Yes, I think this is a reasonable argument for adding a 'slots' option (off by default) for @dataclass(). However I don't think we need to rush it in. I'm not very happy with the general idea of slots any more, and I think that it's probably being overused, and at the same time I expect that there are a lot of classes with a slots declaration that still have a dict as well, because they inherit from a class without slots.
I'm not sure what to do about docstrings -- I'm not a big user of pydoc and I find help() often too verbose (I usually read the source. Maybe we could add a 'doc' option to field()? That's similar to what we offer for property(). On Thu, Dec 7, 2017 at 12:47 PM, Eric V. Smith <e...@trueblade.com> wrote: > On 12/7/17 3:27 PM, Raymond Hettinger wrote: > ... > > I'm looking for guidance or workarounds for two issues that have arisen. >> >> First, the use of default values seems to completely preclude the use of >> __slots__. For example, this raises a ValueError: >> >> class A: >> __slots__ = ['x', 'y'] >> x: int = 10 >> y: int = 20 >> > > Hmm, I wasn't aware of that. I'm not sure I understand why that's an > error. Maybe it could be fixed? > > Otherwise, I have a decorator that takes a dataclass and returns a new > class with slots set: > > >>> from dataclasses import dataclass > >>> from dataclass_tools import add_slots > >>> @add_slots > ... @dataclass > ... class C: > ... x: int = 0 > ... y: int = 0 > ... > >>> c = C() > >>> c > C(x=0, y=0) > >>> c.z = 3 > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AttributeError: 'C' object has no attribute 'z' > > This doesn't help the general case (your class A), but it does at least > solve it for dataclasses. Whether it should be actually included, and what > the interface would look like, can be (and I'm sure will be!) argued. > > The reason I didn't include it (as @dataclass(slots=True)) is because it > has to return a new class, and the rest of the dataclass features just > modifies the given class in place. I wanted to maintain that conceptual > simplicity. But this might be a reason to abandon that. For what it's > worth, attrs does have an @attr.s(slots=True) that returns a new class with > __slots__ set. > > The second issue is that the different annotations give different >> signatures than would produced for manually written classes. It is unclear >> what the best practice is for where to put the annotations and their >> associated docstrings. >> > > I don't have any suggestions here. > > Eric. > > _______________________________________________ > 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/guido% > 40python.org > -- --Guido van Rossum (python.org/~guido)
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