[Python-Dev] Floor division (original) (raw)

Tim Peters tim.peters at gmail.com
Fri Jan 26 02:15:13 CET 2007

[Guido]

... I don't care about the speed, but having to import math (which I otherwise almost never need) is a distraction, and (perhaps more so) I can never remember whether it's modf() or fmod() that I want.

fractional part of x == fmod(x, 1.0) == modf(x)[0], so you could use either. Since modf returns a tuple and fmod returns a float, you'll get an exception quickly if you pick the wrong one :-) The name "modf" certainly sucks.

...

assuming int() continues to truncate.

Has anyone suggested to change that? I'm not aware of any complaints or problems due to int() truncating. There have been requests to add new kinds of round-to-integer functions, but in addition to int().

I thought those semantics were kind of poorly specified. But maybe that was long ago (when int() just did whatever (int) did in C) and it's part of the language now.

"(int)float_or_double" truncates in C (even in K&R C) /provided that/ the true result is representable as an int. Else behavior is undefined (may return -1, may cause a HW fault, ...).

So Python uses C's modf() for float->int now, which is always defined for finite floats, and also truncates.

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