On Sun, Dec 5, 2021 at 3:08 PM Stephen J. Turnbull email@example.com wrote:
Barry Scott writes:
There are many possible implementation of the late bound idea that could create an object/default expression. But is it reasonable to bother with that added complexity/maintenance burden for a first implementation.
Yes. If you don't do it, you'll have backward compatibility issues or technical debt.
I'm not saying that's a compelling argument here, except that one of the main alleged problems is that users don't understand mutable defaults. So adding more and more layers of support for default arguments is making matters worse, I suspect. (Remember, they're going to be reading "arg=None" and "@arg=" for a long long time.)
This one is Worth Doing Right the first time, I think. And IMO David Mertz is right: doing it right means a more general deferred-evaluation object (not to be confused with Deferreds that need to be queried about their value).
If you think that deferred evaluation objects are the right way to do it, then write up a proposal to compete with PEP 671. In my opinion, it is a completely independent idea, which has its own merit, and which is not a complete replacement for late-bound defaults; the two could coexist in Python simultaneously, or either one could be accepted without the other, or we could continue to have neither. Yes, there's some overlap in the problems they solve, just as there's overlap between PEP 671 and PEP 661 on named sentinels; but there's also overlap between plenty of other language features, and we don't deem try/finally or context managers to be useless because of the other.