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And notice that there is absolutely no difficulty with some future enhancement to allow positional arguments after keyword arguments.
We've already discussed in this thread that we shouldn't fear conflicting with other (real or hypothetical) proposals, even if they're likely. As I see it, the chance of allowing positional arguments after keyword arguments is basically zero. The restriction is intentionally there for a good reason. And quoting your next message: All else being equal, we should prefer the syntax that doesn't rule out
future development.
I don't think all else is equal. I think the downside of a pseudo-expression far, far outweighs the downside of conflicting with unlikely hypothetical future proposals. Also, the way you're arguing against possibly conflicting with some future enhancement, I'm not sure why you'd ever support said enhancement, given that it would still potentially conflict with other possible enhancements in the even more distant future.