On Friday, March 6, 2015 at 10:29:19 PM UTC+5:30, Steven D'Aprano wrote: > Rustom Mody wrote: > > > On Friday, March 6, 2015 at 3:31:58 PM UTC+5:30, Chris Angelico wrote: > >> On Fri, Mar 6, 2015 at 8:50 PM, Rustom Mody wrote: > >> > In a language like python with decent exceptions we do not need nans. > >> > >> Not so. I could perhaps accept that we don't need signalling NaNs, as > >> they can be replaced with exceptions, but quiet NaNs are by definition > >> _not_ exceptions. > > > > My impression (maybe I am wrong): > > "Catch an exception and ignore it" is a way of converting signalling to > > quiet With the added advantage of being able to tweak the specs of what > > happens when nan op normal to one's taste > > > I don't understand what you are trying to say. > > Let's take a dirt-simple example: > > def inverse(x): > return 1.0/x > > There's an exception there, waiting to bite. If I include inverse() in some > complex calculation: > > def function(x, y): > return atan2(inverse(3*x*y)+1, inverse(1 - x**2 + 3*x - 0.2)**3) > > values = [function(1.5*x, y+2) for x, y in zip(xx, yy)] > > and I just wish to skip over the failed calculations, I can't just "ignore" > exceptions: > > # This doesn't work! > def inverse(x): > try: > return 1.0/x > except ZeroDivisionError: > pass > > > I have to return something that acts like a number but isn't a number. > > Something which, once it enters a calculation, should propagate through it. > But not necessarily something which once it enters can never be removed! It > may be that some calculations can "cancel out" these "errors" (indeed, the > atan2 function is one of those -- it can return non-NANs from at least some > NAN arguments). So what should I return? It cannot be a number, but it has > to act like a number. Ideally, it should carry diagnostic information so I > can see what the failure was, for debugging, although I may not bother to > do so that information should at least be available for use. > > I have just re-invented NANs.
Ok... Maybe so As I said I am not too sure about this However you have to give me a little fuller (if not more realistic) example [Your xx and yy are what?] And I have to see if I know how to tweak it nan-less And at least maintain hopefully improve the clarity, succinctness of the original! Not saying I will be able -- just that thats the claim -- https://mail.python.org/mailman/listinfo/python-list
