On Sun, Feb 4, 2018 at 7:54 PM, Nick Coghlan <ncogh...@gmail.com> wrote:
> On 5 February 2018 at 08:31, Guido van Rossum <gu...@python.org> wrote: > > On Sun, Feb 4, 2018 at 11:59 AM, Chris Barker - NOAA Federal > > <chris.bar...@noaa.gov> wrote: > >> > >> I think the folks that are concerned about this issue are quite right > >> — most Python users equate immutable and hashable—so the dataclass API > >> should reflect that. > > > > Since they are *not* equivalent (consider a tuple containing a list) I'm > not > > at all convinced that any API in the core language should "reflect" this > > misconception, depending on how you meant that. > > Lists are themselves mutable, and hence inherently unhashable. > > Tuples are themselves immutable, and hence hashable if their contents are. > > I interpret Chris's comment as saying that data classes should behave > the same way that the builtin container types do: > pretty much, yes, But a bit more detail -- I'm commenting on the API, not the capability - that is, since users often equate hashable and immutability, they will expect that if they say hash=True, then will get an immutable, and if they say frozen=True, they will get something hashable (as long as the fields are hashable, just like a tuple. That is, even though these concepts are independent, the defaults shouldn't reflect that. It's the ability to ask the interpreter to guess what you mean > "frozen=False, hash=True" that creates the likelihood of confusion. > Actually, I think if the user does explicitly specify: "frozen=False, hash=True", then that's what they should get, and it's a pretty fragile beast, but apparently there's enough of a use case for folks to want it, and I don't think it's a confusing API. -CHB -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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