On 12/05/2022 01.33, Michael F. Stemper wrote: > I have a function that I use to retrieve daily data from a > home-brew database. Its calling sequence is; > > def TempsOneDay( year, month, date ): > > After using it (and its friends) for a few years, I've come to > realize that there are times where it would be advantageous to > invoke it with a datetime.date as its single argument. > > As far as I can tell, there are three ways for me to proceed: > 1. Write a similar function that takes a single datetime.date > as its argument. > 2. Rewrite the existing function so that it takes a single > argument, which can be either a tuple of (year,month,date) > or a datetime.date argument. > 3. Rewrite the existing function so that its first argument > can be either an int (for year) or a datetime.date. The > existing month and date arguments would be optional, with > default=None. But, if the first argument is an int, and > either of month or date is None, an error would be raised. > > The first would be the simplest. However, it is obviously WET > rather than DRY. > > The second isn't too bad, but a change like this would require that > I find all places that the function is currently used and insert a > pair of parentheses. Touching this much code is risky, as well > as being a bunch of work. (Admittedly, I'd only do it once.) > > The third is really klunky, but wouldn't need to touch anything > besides this function. > > What are others' thoughts? Which of the approaches above looks > least undesirable (and why)? Can anybody see a fourth approach?
Reading the above, it seems that the options are limited to using positional-arguments only. Because I keep tripping-over my long, grey, beard; I'm reminded that relying upon my/human memory is, um, unreliable (at least in my case). Accordingly, by the time a function's definition reaches three parameters, I'll be converting it to use keyword-arguments as a matter of policy. YMMV! Remember: if keyword arguments are not used (ie existing/legacy code), Python will still use positional logic. Once the function's signature has been changed, we could then add another keyword-parameter to cover the datetime option. That said, a function which starts with a list of ifs-buts-and-maybes* which are only there to ascertain which set of arguments have been provided by the calling-routine; obscures the purpose/responsibility of the function and decreases its readability (perhaps not by much, but varying by situation). Accordingly, if the function is actually a method, recommend following @Stefan's approach, ie multiple-constructors. Although, this too can result in lower readability. Assuming it is a function, and that there are not many alternate APIs/approaches (here we're discussing only two), I'd probably create a wrapper-function which has the sole task of re-stating the datetime whilst calling the existing three-parameter function. The readability consideration here, is to make a good choice of (new) function-name! * Python version >= 10? Consider using match-case construct keyed on parameter-type -- Regards, =dn -- https://mail.python.org/mailman/listinfo/python-list
