Re: cpython list __str__ method for floats
[david] wrote: Leaving aside the question of why str should return repr, str doesn't return repr. str returns a nice string representation of an object. This nice string representation of a list is the opening square bracket, the repr of its contents seperated by comma, and the closing square bracket. prayer-millHere, it *only* makes sense to have a list printed with the repr of their contents./prayer-mill 13.301 is not 'the float in full precision': it is an arbitrary translation of the float. Do you know IEEE 754? The idea that 13.3 is a 'rounded' value for the number, and that 13.301 is not a 'rounded' value of the number, is a common error of intuitive mathematics. I'm intrigued how /you/'d explain this, please do explain. I hope that when you say that this is a FAQ, you don't mean that the community has solidified on this naive interpretation :~) No, I mean that your complaint is not at all new. Reading the archives you could have learned a lot about this topic. Regards, Björn -- BOFH excuse #247: Due to Federal Budget problems we have been forced to cut back on the number of users able to access the system at one time. (namely none allowed) -- http://mail.python.org/mailman/listinfo/python-list
Re: cpython list __str__ method for floats
Bjoern Schliessmann [EMAIL PROTECTED] wrote: The idea that 13.3 is a 'rounded' value for the number, and that 13.301 is not a 'rounded' value of the number, is a common error of intuitive mathematics. I'm intrigued how /you/'d explain this, please do explain. I think he is correct here: 13.301 is not exactly representable in IEEE 754. It is a rounded approximation to the true value just as is 13.3. An argument can be made that instead of rounding the internal value to 17 digits which is sufficient to ensure that you can roundtrip float- string-float for all values, you could just round it to the minimum number of digits which guarantee the float-string-float roundtrip for that particular value. Consider this as we gradually lose the more significant digits we see that last digit wasn't exactly 1 at all: 13.3 13.301 13.3-13 0.30071 (13.3-13)*10-3 7.1054273576010019e-015 but why shouldn't Python do this instead?: 13.3 13.3 13.3-13 0.3 (13.3-13)*10-3 7.1054273576e-015 These values will still roundtrip to the exact same internal representations. BTW, I didn't have to work too hard to figure out what that last value should be, the first is cut/paste from CPython, the second is what IronPython gives you. I believe the claim is that using the full 17 digits ensures the round- tripping works even if you serialise and deserialise on different systems, so perhaps we all pay a cost in our interactive sessions for something which should really be buried deep in IPC code. -- http://mail.python.org/mailman/listinfo/python-list
Re: cpython list __str__ method for floats
On Sep 12, 10:59 pm, Duncan Booth [EMAIL PROTECTED] wrote: [snip] I believe the claim is that using the full 17 digits ensures the round- tripping works even if you serialise and deserialise on different systems, so perhaps we all pay a cost in our interactive sessions for something which should really be buried deep in IPC code. IPC? Most data transfer between systems in the real world is done using CSV files :-) -- http://mail.python.org/mailman/listinfo/python-list
cpython list __str__ method for floats
returns poorly formatted values: str(13.3) '13.3' str([13.3]) '[13.301]' [david] -- http://mail.python.org/mailman/listinfo/python-list
Re: cpython list __str__ method for floats
On Sep 11, 4:07 am, [david] [EMAIL PROTECTED] wrote: returns poorly formatted values: str(13.3) '13.3' str([13.3]) '[13.301]' [david] There is some difference in the way repr() and str() convert floats to strings: a = 13.3 print str(a) 13.3 print repr(a) 13.301 a 13.301 a.__str__() '13.3' a.__repr__() '13.301' -- http://mail.python.org/mailman/listinfo/python-list
Re: cpython list __str__ method for floats
[david] wrote: returns poorly formatted values: Please explain. str(13.3) '13.3' str([13.3]) '[13.301]' This is quite a FAQ. str of a float returns the float, rounded to decimal precision. str of a list returns a square brackets enclosed enumeration of the contents (using repr on them). repr of a float returns the float in full precision. Regards, Björn -- BOFH excuse #442: Trojan horse ran out of hay -- http://mail.python.org/mailman/listinfo/python-list
Re: cpython list __str__ method for floats
Bjoern Schliessmann wrote: [david] wrote: returns poorly formatted values: Please explain. str(13.3) '13.3' str([13.3]) '[13.301]' This is quite a FAQ. str of a float returns the float, rounded to decimal precision. str of a list returns a square brackets enclosed enumeration of the contents (using repr on them). repr of a float returns the float in full precision. Regards, Björn contents (using repr on them). repr of a float returns the float in full precision. But of course it doesn't, as illustrated, which is the whole point. It returns a string at greater than full precision. Leaving aside the question of why str should return repr, 13.301 is not 'the float in full precision': it is an arbitrary translation of the float. The idea that 13.3 is a 'rounded' value for the number, and that 13.301 is not a 'rounded' value of the number, is a common error of intuitive mathematics. I hope that when you say that this is a FAQ, you don't mean that the community has solidified on this naive interpretation :~) [david] -- http://mail.python.org/mailman/listinfo/python-list
