On Sat, 1 Sep 2018 at 12:31, Frank Millman <fr...@chagford.com> wrote: > > "Frank Millman" wrote in message news:pm3l2m$kv4$1...@blaine.gmane.org... > > > > I know about this gotcha - > > > > >>> x = 1.1 + 2.2 > > >>> x > > 3.3000000000000003 > > > [...] > > I have enjoyed the discussion, and I have learnt a lot about floating point. > Thanks to all. > > I have just noticed one oddity which I thought worth a mention. > > >>> from decimal import Decimal as D > >>> f"{D('1.1')+D('2.2'):.60f}" > '3.300000000000000000000000000000000000000000000000000000000000' > >>> '{:.60f}'.format(D('1.1') + D('2.2')) > '3.300000000000000000000000000000000000000000000000000000000000' > >>> '%.60f' % (D('1.1') + D('2.2')) > '3.299999999999999822364316059974953532218933105468750000000000' > >>> > > The first two format methods behave as expected. The old-style '%' operator > does not. > > Frank
Presumably, Decimal has a custom formatting method. The old-style % formatting doesn't support custom per-class formatting, so %.60f converts its argument to float and then prints it. Paul -- https://mail.python.org/mailman/listinfo/python-list
