[Python-ideas] Fwd: Make `float('inf') //1 == float('inf')`

[Petr Viktorin]

For the record, this gives inf in Numpy.

>>> import numpy
>>> numpy.array(float('inf')) // 1
inf

AFAIK this and http://bugs.python.org/issue22198 are the only
differences from Python floats, at least on my machine.


On Thu, Sep 18, 2014 at 12:08 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 18 September 2014 07:52, Ian Cordasco <graffatcolmingov at gmail.com> wrote:
>> Actually there are 2 things here:
>>
>> 1. Mathematically speaking, infinity is a real number and modulo
>> arithmetic is algebraically not defined for it. So the "mathematically
>> reasonable value" is NaN. Is it intuitive for someone who hasn't
>> studied abstract algebra? Probably not. Is it functional for the
>> scientific python community? Almost certainly although I won't pretend
>> to speak on their behalf
>
> Right, as with NaN, infinity is a concept rather than a value. The
> fact that they both map to "kinda sorta values" in a programming
> language like Python is a limitation of the computer's underlying
> representational system, and the end result is a leaky abstraction
> that has some weird artefacts like this one (the fact that key lookup
> based containers enforce reflexivity, even though floating point NaN
> comparisons are explicitly defined as non-reflexive, is another).
>
> There's no real way to make floating point arithmetic "not surprising"
> as soon as NaN and infinities get involved (while I'd be surprised if
> anyone was inclined to dispute that, here's a fun link on the
> "infinite values" side that will hopefully deter the unduly
> optimistic: https://en.wikipedia.org/wiki/Aleph_number).
>
>> 2. Changing this behaviour is not something I think we should do in a
>> minor version of 3.4 or in 3.5 (or really 3.x).
>
> For a topic as inherently confusing as infinite values, I believe it
> would take a battery of extensive usability studies to make the case
> that any change in behaviour from the status quo would be worth the
> hassle, and most researchers are going to have more interesting things
> to do with their time.
>
> Some of the things we changed in the Python 3 transition (like
> rearranging modules) were based on intuition as to what would be
> easier for newcomers to learn, and if I learned anything from that,
> it's to rely more heavily on the ethos of "status quo wins a
> stalemate" when it comes to the way we represent concepts that are
> just plain hard to learn in their own right.
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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