On Thu, Dec 2, 2021 at 7:31 PM Paul Moore <p.f.mo...@gmail.com> wrote:
>
> On Wed, 1 Dec 2021 at 22:27, Greg Ewing <greg.ew...@canterbury.ac.nz> wrote:
> >
> > On 2/12/21 4:40 am, Paul Moore wrote:
> > > the
> > > intended use is that people must supply a list[int] or not supply the
> > > argument *at all*.
> >
> > I don't think this is a style of API that we should be encouraging
> > people to create, because it results in things that are very
> > awkward to wrap.
>
> Hmm, interesting point, I agree with you. It's particularly telling
> that I got sucked into designing that sort of API, even though I know
> it's got this problem. I guess that counts as an argument against the
> late bound defaults proposal - or maybe even two:
>
> 1. It's hard (if not impossible) to wrap functions that use late-bound
> defaults.
> 2. The feature encourages people to write such unwrappable functions
> when an alternative formulation that is wrappable is just as good.
>
> (That may actually only be one point - obviously a feature encourages
> people to use it, and any feature can be over-used. But the point
> about wrappability stands).
>
Wrappability when using an arbitrary sentinel looks like this:
_SENTINEL = object()
def f(value=_SENTINEL):
if value is _SENTINEL: value = ...
# in another module
def wrap_f():
othermodule.f(othermodule._SENTINEL)
Or:
def wrap_f():
othermodule.f(othermodule.f.__defaults__[0])
I'm not sure either of these is any better than the alternatives.
You're reaching into a module to access its internal implementation
details. Is that really better than messing with *args?
def wrap_f():
args = [42] or [] # pass or don't pass?
othermodule.f(*args)
It only looks easy when None is used, and even then, it's largely an
implementation detail.
ChrisA
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