Mark Dickinson added the comment: Actually, there are two potential sources of confusion here:
1. Python uses the round-ties-to-even rounding mode, which means cases that are *exactly* halfway between two target values round to the value with even last digit. This rule is being used in your first example (4.625), which is a value that's exactly representable in the IEEE 754 binary64 format that Python typically uses to represent floats, and is exactly halfway between 4.2 and 4.3. 2. It might look as though round-ties-to-even applies in the second and third cases, too, but that's not the case, since these values *aren't* exactly halfway between the relevant decimal values, thanks to the representation error incurred when translating to the binary64 format. The value specified by the literal "4.645" is stored internally as "4.644999999999999573674358543939888477325439453125", which is a tiny amount closer to 4.64 than to 4.65, so it rounds to 4.64. The value 4.655 works similarly. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue30453> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
