On Wed, Oct 27, 2021 at 8:06 AM Erik Demaine <edema...@mit.edu> wrote:
> I wonder if it would make sense to offer a "missing argument" object (builtin?
> attribute of inspect.Parameter? attribute of types.FunctionType?) that
> actually simulates the behavior of that argument not being passed. Let me
> call it `_missing` for now. This would actually make it far easier to
> accomplish "pass in the second argument but not the first", both with early-
> and late-binding defaults:
>
> ```
> f(_missing, {'more'})
> g(_missing, {'more'})
> ```
>
> I started thinking about `_missing` when thinking about how to implement
> late-binding defaults. It's at least one way to do it (then the function
> itself could even do the argument checks), though perhaps there are simpler
> ways that avoid the ref count increments.
>
The trouble with sentinel values is that you always need another one.
Sooner or later, you're going to need to talk about the _missing
object, and you'll need to distinguish it from the absence of an
object.
If there is a way to say "don't pass this argument", it would have to
be some kind of syntactic token.
ChrisA
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