[Python-ideas] Suggestion: Extend integers to include iNaN

[Oscar Benjamin]

On Mon, 1 Oct 2018 at 00:00, Chris Angelico <rosuav at gmail.com> wrote:
>
> On Mon, Oct 1, 2018 at 8:53 AM Oscar Benjamin
> <oscar.j.benjamin at gmail.com> wrote:
> >
> > On Sun, 30 Sep 2018 at 02:01, Steven D'Aprano <steve at pearwood.info> wrote:
> > >
> > > On Sat, Sep 29, 2018 at 09:43:42PM +0100, Oscar Benjamin wrote:
> > > > On Sat, 29 Sep 2018 at 19:38, Steve Barnes <gadgetsteve at live.co.uk> wrote:
> > >
> > > > > > I converted to int because I needed a whole number, this was intended to
> > > > > represent some more complex process where a value is converted to a
> > > > > whole number down in the depths of the processing.
> > > >
> > > > Your requirement to have a whole number cannot meaningfully be
> > > > satisfied if your input is nan so an exception is the most useful
> > > > result.
> > >
> > > Not to Steve it isn't.
> > >
> > > Be careful about making value judgements like that: Steve is asking for
> > > an integer NAN because for *him* an integer NAN is more useful than an
> > > exception. You shouldn't tell him that he is wrong, unless you know his
> > > use-case and his code, which you don't.
> >
> > Then he can catch the exception and do something else. If I called
> > int(x) because my subsequent code "needed a whole number" then I would
> > definitely not want to end up with a nan. The proposal requested is
> > that int(x) could return something other than a well defined integer.
> > That would break a lot of code!
>
> At no point was the behaviour of int(x) ever proposed to be changed.
> Don't overreact here.

The context got trimmed a bit too much. You can see here the messages
preceding what is quoted above:
https://mail.python.org/pipermail/python-ideas/2018-September/053840.html

Quoting here:
> One simplistic example would be print(int(float('nan'))) (gives a ValueError) while print(int(iNaN)) should give 'nan' or maybe 'inan'

That would mean that the result of int(x) is no longer guaranteed to
be a well-defined integer.

> The recommended use-case was for a library to
> return iNaN instead of None when it is unable to return an actual
> value.

You can already use None or float('nan') for this. You can also create
your own singleton nan object if you want. When I said I haven't seen
a use-case what I mean is that no one has presented a situation where
the existing language facilities are considered insufficient (apart
from the suggestion about int(iNaN) that I refer to above).

--
Oscar