@zhangyangyu, thanks for your PR! By analyzing the history of the files in this pull request, we identified @serhiy-storchaka, @jackjansen and @benjaminp to be potential reviewers.

Of course I could add a test. I don't think we need a doc. It's never mentioned in the current doc and actually I think nobody notice the unintentional change.

I'm not sure about tests. Other implementation can support passing data as keyword, this isn't a bug. It is hard to implement positional-only parameter in pure Python.

Honestly speaking I support adding a test in this case. There are already some tests for positional-only arguments in other tests. I am not sure we should take care of other implementation here or this needs a cpython-only test.

What are other tests for positional-only arguments?

Like test_builtin.TestSorted.test_bad_arguments.

test_builtin.TestSorted.test_bad_arguments tests a concrete bug caused a crash when pass the first argument by keyword. This is an exceptional case.

The change looks like it does what is intended, although I don’t think it is worthwhile. The damage (if any) as already been done.

Okay. Remove the test. Thanks all :-)