On Fri, 31 Aug 2018 18:45:16 +1200, Gregory Ewing wrote: > Steven D'Aprano wrote: >> The right way is to >> set the rounding mode at the start of your application, and then let >> the Decimal type round each calculation that needs rounding. > > It's not clear what you mean by "rounding mode" here. If you mean > whether it's up/down/even/whatever, then yes, you can probably set that > as a default and leave it.
I mean the rounding mode :-) https://docs.python.org/3/library/decimal.html#rounding-modes > However, as far as I can see, Decimal doesn't provide a way of setting a > default number of decimal places to which results are rounded. You can > set a default *precision*, but that's not the same thing. Indeed it is not. That's a very good point, and I had completely forgotten about it! Thank you. The quantize method is intended for the use-case we are discussing, to round values to a fixed number of decimal places. The Decimal FAQs mention that: https://docs.python.org/3/library/decimal.html#decimal-faq I think this is a good use-case for subclassing Decimal as a Money class. [...] > I don't think this is a bad thing, because often you don't want to use > the same number of places for everything, For example, people dealing > with high-volume low-value goods often calculate with unit prices having > more than 2 decimal places. In those kinds of situations, you need to > know exactly what you're doing every step of the way. As opposed to anyone else calculating with money? -- Steven D'Aprano "Ever since I learned about confirmation bias, I've been seeing it everywhere." -- Jon Ronson -- https://mail.python.org/mailman/listinfo/python-list
