On Thu, Dec 2, 2021 at 12:42 PM David Lukeš <dafydd.lukes@gmail.com> wrote:

...

That's an oversimplification:

foo = 42 def bar(): print(foo) foo = 1

This won't print 42.

Oh, right. I've run afoul of this in the past, but clearly not often enough to make it second nature :) Thanks for being helpful!

I still think nudging people to only refer to previous arguments in their late-bound defaults is a good idea though, for readability and intuitiveness.

Oh yes, absolutely. Whether it's legal or not, referring to future arguments will always be frowned upon.

Maybe a good way to enforce it naturally (at least w.r.t. to arguments without late-bound defaults) would be via a similar syntax as keyword-only arguments? Something like:

def foo(bar, *, baz=1, @, qux=[baz]): ...

That's rather restricting, and it implies that there's a major difference in the way that functions would be defined ("late-bound default keyword-only arguments" would become a brand new type of argument) rather than a small difference in the way a function default is defined.

Now that I look at it, I actually like this bikeshed quite a lot. It trades some of the flexibility for expliciteness (the @ is very conspicuous in this position), consistency and predictability, which feels Pythonic. The @-as-barrier-to-eager-evaluation mnemonic still works. No potential => footgun.

But it's late at night and I need to go to bed, so I probably messed something up again?

Not messed up, other than the fact that it's more change than I think this needs. :) ChrisA