The futures case is one example of a broader API design issue.

Note also that 'self' is similarly restricted.  You might think these are 'corner cases', but to me it is poor API design.  There may well be a reasonable case for passing 'self' as a keyword arg; what right has the API to dictate otherwise?

I think Python's private name mangling provides a reasonably clean, self-documenting solution, pushing the 'corner' case further to the corner (the restriction would then be on the much-less-likely mangled names).