Steven D'Aprano wrote:
The advantage of F being callable is that it does not need semantic change, the filtering part will be done before expression just like it is right now.
That's not true. It can't be true. If you want to filter on x**x being greater than 100, you need to calculate x**x first. In theory, a sufficiently clever compiler could recognise that, say, x**x < 100 implies 0 <= x < 3.59728 (approx), but in general, you can't predict the value of f(x) without actually calculating f(x).
Did you read the middle part of the post and the diagram, which address the question you're asking and how it would be handled?
What happens if you accidentally forget to put brackets after the F expression? Do you get a syntax error? Undefined behaviour? A runtime exception?
As F is just callable, F > 100 should result in comparison of number against callable. But as it is rare that you really actually wanted to do such thing, I think python can also be a little protective and issue a warning.