[Python-Dev] Python's C interface for types (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Sat Jan 27 00:43:06 CET 2007

Nick Maclaren schrieb:

I personally consider very important that hash(5.0) == hash(5) (and that 5.0 == 5, of course). It gets a bit problematic with floating-point, when you can have different values "exactly 5.0" and "approximately 5.0". IEEE 754 has signed zeroes. And so it goes.

[not sure what "And so it goes" means in English]

It may be a bit problematic to implement, but I think a clean specification is possible. If a and b are numbers, and a==b, then hash(a)==hash(b). I'm not sure whether "approximately 5.0" equals 5 or not: if it does, it should hash the same as 5, if it doesn't, it may or may not hash the same (whatever is easier to implement). For 0: hash(+0.0)==hash(-0.0)==hash(0)=hash(0L)=0

Regards, Martin

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