On Mon, Oct 25, 2021 at 3:12 PM Sebastian Berg <sebast...@sipsolutions.net> wrote: > > On Mon, 2021-10-25 at 03:47 +1100, Chris Angelico wrote: > > On Mon, Oct 25, 2021 at 3:43 AM Jonathan Fine <jfine2...@gmail.com> > > wrote: > > > > > > Hi > > > > > > Please forgive me if it's not already been considered. Is the > > > following valid syntax, and if so what's the semantics? Here it is: > > > > > > def puzzle(*, a=>b+1, b=>a+1): > > > return a, b > > > > > > Aside: In a functional programming language > > > a = b + 1 > > > b = a + 1 > > > would be a syntax (or at least compile time) error. > > > > > > > I was about to ask about this. But also, how does that go together > with non-required arguments? > > def function(arr=>np.asarray(arr)): > pass > > Would seem like something we may be inclined to write instead of: > > def function(arr): > arr = np.asarray(arr) > > (if that is legal syntax). In that case `arr` is a required parameter. > Which then means that you cannot do it for optional parameters?:
This is all about argument defaults, not transforming values that were passed in. So if you pass a value, you always get exactly that value. > def function(arr1=>np.asarray(arr), arr2=>something): > arr2 = np.asarray(arr2) # in case arr2 was passed in > > Which is fair, but feels like a slightly weird difference in usage > between required and optional arguments? > > > There are two possibilities: either it's a SyntaxError, or it's a > > run-time UnboundLocalError if you omit both of them (in which case it > > would be perfectly legal and sensible if you specify one of them). > > > > I'm currently inclined towards SyntaxError, since permitting it would > > open up some hard-to-track-down bugs, but am open to suggestions > > about > > how it would be of value to permit this. > > Not sure that I am scared of this if it gives a clear exception: > > Parameter `a` was not passed, but it can only be omitted when > parameter `b` is passed. > > Not as clear (or complete) as a custom message, but not terrible? > A tad complicated and would require some hairy analysis. Also, I don't really want to encourage argument defaults that depend on each other :) ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/VVPNAWCKAGBROZSBGQUWDFGZGYMET2NW/ Code of Conduct: http://python.org/psf/codeofconduct/
