[Python-Dev] trunc() (original) (raw)
Jeffrey Yasskin jyasskin at gmail.com
Fri Jan 25 00:14:56 CET 2008
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On Jan 24, 2008 1:09 PM, Daniel Stutzbach <daniel at stutzbachenterprises.com> wrote:
On Jan 24, 2008 12:46 PM, Guido van Rossum <guido at python.org> wrote: > trunc() has well-defined semantics -- it takes a Real instance and > converts it to an Integer instance using round-towards-zero semantics. > > int() has undefined semantics -- it takes any object and converts it > to an int (a concrete type!) using whatever rules it likes -- the > definition of int is up to whatever the source type likes to do.
What are the use-cases for when trunc() vs int() should be used, and for when a class should define trunc vs int?
If you intend to convert a real number (usually float, since Decimal has decided not to support it) to an Integral (usually int), use whichever of trunc(), round(), math.floor(), or math.ceil() you intend. In 2.6, that list only includes trunc(). If you absolutely need an int (the concrete, not duck type) from an Integral or you want to parse a string, use int().
Real numbers should define trunc. Integrals and, perhaps, some string-like types (maybe an MD5 class?) should define int.
At least, that's my suggestion.
-- Namasté, Jeffrey Yasskin
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