[Python-Dev] Return type of round, floor, and ceil in 2.6 (original) (raw)

Jeffrey Yasskin jyasskin at gmail.com
Sun Jan 6 10:50:42 CET 2008

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On Jan 5, 2008 4:20 PM, Tim Peters <tim.peters at gmail.com> wrote:

[Guido] > Wow. Do you have an opinion as to whether we should adopt > round-to-even at all (as a default)?

Yes: yes :-)

Thanks for the suggestion, Tim. Here's a new proposed patch to the pep. It still allows type-defined half-rounding behavior so that Decimal can follow the current context. I'll submit it tomorrow unless there are significant objections.

Index: pep-3141.txt

--- pep-3141.txt (revision 59739) +++ pep-3141.txt (working copy) @@ -205,8 +205,12 @@ def round(self, ndigits:Integral=None): """Rounds self to ndigits decimal places, defaulting to 0.

•        If ndigits is omitted or None, returns an Integral, otherwise

•        returns a Real. Rounds half toward even.

•        If ndigits is omitted or None, returns an Integral,

•        otherwise returns a Real, preferably of the same type as

•        self. Types may choose which direction to round half. For

•        example, float rounds half toward even, and Decimal rounds

•        it according to the current context.

•         """
          raise NotImplementedError

@@ -428,10 +432,14 @@ least Integral >= x.

1. __round__(self), called from round(x), which returns the

• Integral closest to x, rounding half toward even. There is also
• a 2-argument version, __round__(self, other), called from
• round(x, y), which should return a Real.

• Integral closest to x, rounding half as the type chooses.
• float will change in 3.0 to round half toward even. There is
• also a 2-argument version, __round__(self, ndigits), called
• from round(x, ndigits), which should return a Real.

+In 2.6, math.floor, math.ceil, and round will continue to +return floats. + Because the int() conversion implemented by float (and by decimal.Decimal) is equivalent to but less explicit than trunc(), let's remove it. (Or, if that breaks too much, just add a

-- Namasté, Jeffrey Yasskin

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