On Mon, Sep 13, 2021 at 1:37 AM Serhiy Storchaka <storchaka@gmail.com> wrote:
12.09.21 17:28, Guido van Rossum пише:
This is cool.
AFAIK pytest does something like this. How does your implementation differ?
What pytest does is awesome. I though about implementing it in the standard compiler since seen it the first time.
What is your argument for making this part of the language? Why not a 3rd party library?
It needs a support in the compiler. The condition expression should be compiled to keep all immediate results of subexpressions on the stack. If the final result is true, immediate results are dropped. If it is false, the second argument of assert is evaluated and its value together with all immediate results of the first expression, together with references to corresponding subexpressions (as strings, ranges or AST nodes) are passed to the special handler. That handler can be implemented in a third-party library, because formatting and outputting a report is a complex task. The default handler can just raise an AttributeError.
I wonder, could this be simplified a bit, on the assumption that a well-written assertion shouldn't have a problem with being executed twice? Instead of keeping all the subexpressions around (a run-time cost), keep the AST of the expression itself (a compile-time cost). Then, when the exception is about to be printed to the console, re-evaluate it and do the display. ChrisA