On Thu, Jul 29, 2010 at 8:16 PM, Raymond Hettinger <raymond.hettin...@gmail.com> wrote: > > On Jul 29, 2010, at 11:47 AM, Mark Dickinson wrote: > >> Now that we've got the short float repr in Python, there's less value >> in having float.__str__ truncate to 12 significant digits (as it >> currently does). For Python 3.2, I propose making float.__str__ use >> the same algorithm as float.__repr__ for its output (and similarly for >> complex). > > When you proposed the idea at EuroPython, it seemed reasonable > but we didn't go into the pros and cons. The downsides include > breaking tests, changing the output of report generating scripts > that aren't using string formatting, and it introduces another > inter-version incompatibility.
Yes, I agree that the change has potential for breakage; it's a change that probably would have been unacceptable for Python 2.7; for Python 3.2 I think there's a little more scope, since 3.x has fewer users. And those users it does have at the moment are the early adopters, who with any luck may be more tolerant of this level of breakage. (By the time we get to 3.2 -> 3.3 that's probably not going to be true any more.) Really, this change should have gone into 3.1. FWIW, the change broke very few of the standard library tests (as Eric Smith verified): there was a (somewhat buggy) doctest in test_tokenize that needed fixing, and test_unicodedata computes a checksum that depends on the str() of various numeric values. Apart from those, only test_float and test_complex needed fixing to reflect the __str__ method changes. > The only obvious advantage is > that it makes float.__repr__ and float.__str__ the same, making > one less thing to explain. Can you elaborate on other advantages? > Is there something wrong with the current way? That's one advantage; as mentioned earlier the difference between str and repr causes confusion for floats in containers, where users don't realize that two different operations are being used. This is a genuine problem: I've answered questions about this a couple of times on the #python IRC channel. Another advantage is that is makes 'str' faithful: that is, if x and y are distinct floats then str(x) and str(y) are guaranteed distinct. I know I should know better, but I've been bitten by the lack of faithfulness a couple of times when debugging floating-point problems: I insert a "print(x, y)" line into the code for debugging purposes and still wonder why my 'assertEqual(x, y)' test is failing even though x and y look the same; only then do I remember that I need to use repr instead. As you say, it's just one less surprise, and one less thing to explain: a small shrinkage of the mental footprint of the language. Mark _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com