On Mar 10, 2017 02:42, "Terry Reedy" <tjre...@udel.edu> wrote:
On 3/2/2017 3:03 AM, Serhiy Storchaka wrote: > Function implemented in Python can have optional parameters with default > value. It also can accept arbitrary number of positional and keyword > arguments if use var-positional or var-keyword parameters (*args and > **kwargs). > In other words, Python signature possibilities are already unusually complex. But there is no way to declare an optional parameter that > don't have default value. > ... [moving the following up] > I propose to add a new syntax for optional parameters. If the argument > corresponding to the optional parameter without default value is not > specified, the parameter takes no value. -1 Being able to do this would violate what I believe is the fundamental precondition for python-coded function bodies: all parameters are bound to an object (so that using a parameter name is never a NameError); all arguments are used exactly once in the binding process; the binding is done without ambiguity (or resort to disambiguation rules). Calls that prevent establishment of this precondition result in an exception. This precondition is normal in computing languages. I believe that all of the ~20 languages I have used over decades have had it. In any case, I believe it is important in understanding Python signatures and calls, and that there would need to be a strong reason to alter this precondition. (Stronger than I judge the one given here to be.) -1 also Having used a language extensively that does not enforce this precondition (MATLAB), I agree that not being able count on arguments existing makes handing function arguments much more difficult.
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