[Python-Dev] Re: Future division detection

[Christopher A. Craig]

"Tim Peters" <tim.one@home.com> writes:

> [Christopher A. Craig, playing with modifying the meaning of division]
> > ...
> > While doing this I was thinking that I would change true_division on
> > ints and floats to return a rational and change the rational code to
> > return a long if the denominator is 1.  This works great, except that
> > if future division is off then rationals can suddenly become longs and
> > do not automatically cast back.  This makes it virtually impossible to
> > guarantee a correct result to nearly any rational computation that
> > involves a division.
> >
> > So I wanted to know if there is some way to detect, at the object
> > level, if the CO_FUTURE_DIVISION feature is active.
> 
> I'm unclear on what you're asking.  In case it helps, note this section in
> __future__.py:
> 

Hmm, I thought I was being too verbose, I guess I was being too
unclear.  I have a rational module (in C) which I am trying to patch
to be an object satisfying PEP-239.  The problem is that I would like
to have an rational cast back to a integer iff (1) the denominator is 1
and (2) future division is active.

If I don't check (2) then I get the situation that if future division
is inactive then `(rational('1/3')*3)/5` would yield 0 instead of 1/5.
This makes rationals pretty much useless unless future division is
active.

What I would like to do is have a function that can check to see if
the CO_FUTURE_DIVISION flag is set and if it is and the denominator is
1 then return the numerator, else return the rational.

I have a strong suspicion that this can't be done, in which case I
just won't do the cast back automatically.

-- 
Christopher A. Craig <com-nospam@ccraig.org>