[Python-Dev] Deprecating float.is_integer()

[Chris Barker]

On Wed, Mar 21, 2018 at 11:43 PM, Tim Peters <tim.peters at gmail.com> wrote:

> Note:  this is a top-posted essay much more about floating-point
> philosophy than about details.  Details follow from the philosophy,
> and if philosophies don't match the desired details will never match
> either.
>

but of course :-)


> From that fundamental "take floats exactly at face value" view, what
> .is_integer() should do for floats is utterly obvious:


sure -- but I don't think anyone is arguing that -- the question is whether
the function should exist -- and that means not "how should it work?" or
"is it clearly and appropriately defined?" but rather, "is it the "right"
thing to do in most cases, when deployed by folks that haven't thought
deeply about floating point.

> Whether that's _useful_ to you depends on the application you're

> writing at the time.


exactly.

I think pretty much all the real world code that's been shown here for
using .is_integer() is really about type errors (issues). The function at
hand really wants integer inputs -- but wants to allow the user to be
sloppy and provide a float type that happens to be an int. Given Python's
duck-typing nature, maybe that's a good thing? I know I really discourage
dynamic type checking....

Also, every example has been for small-ish integers -- exponents,
factorials, etc -- not order 1e300 -- or inf or NaN, etc.

Finally, the use-cases where the value that happens-to-be-an-int is
computed via floating point -- .is_integer() is probably the wrong check --
you probably want  isclose().

The other use-cases: and floor() and ceil() and round() all produce actual
integers -- so no need for that anymore.

All this points to: we don't need .is_integer

All the being said -- the standard for depreciation is much higher bar than
not-adding-it-in-the-first-place.

-CHB


-- 

Christopher Barker, Ph.D.
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