New submission from Cal Leeming: Hello,
Today I came up against a strange problem where collisions were being encountered after less than 1mil iterations when attempting to use random.random(). After much digging, the problem was because I was casting my float to a string, and this was automatically rounding it. Some explanation is given [1], but it still leaves me with questions. >>> import random >>> random.random() 0.33885573194811902 >>> x = random.random() >>> x 0.88022393777095409 >>> print x 0.880223937771 >>> str(x) '0.880223937771' >>> print str(x) 0.880223937771 >>> repr(x) '0.88022393777095409' >>> str(repr(x)) '0.88022393777095409' After painstakingly searching through documentation (including the lengthy one about floating points arithmetic), I was unable to find any explanation behind why the float is automatically rounded if str() is called on it. Although I doubt this behavior would ever be changed, it would be nice to update the documentation to reflect this. I'm thinking a note underneath random.random() explaining that you have to use repr() and not str() in order to maintain floating point precision. Thoughts? Cal [1] http://stackoverflow.com/questions/3481289/converting-a-python-float-to-a-string-without-losing-precision ---------- components: Interpreter Core messages: 176930 nosy: sleepycal priority: normal severity: normal status: open title: random.random() / float() loses precision when passed to str() versions: Python 2.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue16609> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
