Mark Dickinson <dicki...@gmail.com> added the comment: > print round(2.545, 2) // returns 2.55
Aha! Yes, that one *is* a bug (see issue #1869), though it's not one that I regard as terribly serious, and not one that can be easily solved in all cases. Here's why I don't see it as particularly serious: you're rounding a value that's just on the boundary: 2.545+tiny_error should round up, while 2.545-tiny_error should round down. But tiny (or not-so-tiny) errors are an almost unavoidable part of working with binary floating-point arithmetic. Additionally, whether the binary approximation stored for 2.545 is less than or greater than the true value depends on many things (format of a C double, system C library function used for string-to-double conversion, etc.), so in a sense either 2.55 *or* 2.54 can be defended as a valid result, and a good numeric programmer won't write code that depends on getting one or the other. Having said that, if you're interested in providing a patch for issue #1869 I'd certainly take a look. If you care about *exact* representations of numbers with a finite number of places after the decimal point, you may be interested in Python's 'decimal' module. _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue5118> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
