[Fwd: Comment on PEP-0238]

[Chris Gonnerman]

----- Original Message -----
From: "Guido van Rossum" <guido at digicool.com>


> > However, I think that some details of the numerics also need to
> > be clarified before you boldly go.  Specifically,
> >
> >  - What about long division?  A float cannot capture all results.
> >    Should it raise a Value/Range error?
> >    Should the programmer be forced to use divmod?
> >    Should it return a rational?
> >    I don't really like the last two choices and the first two choices
> >    obviate much of the usefulness of longs.
>
> We'll introduce a new operator or function (e.g. div(x, y)) for
> integer division, which will work for ints and longs.  When / is used
> and the result can't be expressed as a C double, we can choose between
> yielding Infinity or raising OverflowError; I think probably the
> latter although with two float arguments this currently returns Inf on
> most platforms.

Perhaps it's too inconsistent, but I see no reason why longs can't continue
returning "normal" results forever.  When you use a long you know what you
are
doing, or at least think you do; so you should expect integer division
results
just as always.

What does it buy us to break longs as well as ints?

Overall I am in favor of *eventually* automatically promoting ints to float
when division is attempted, and likewise converting longs to floats when
dividing one by the other, but I really think we gain nothing by changing
the semantics of division of longs.

I would also say that, when longs and ints are divided together, you should
probably promote the int to a long rather than performing float division.

In other words:

    int / int => float
    float / float => float
    long / long => long

    int / float => float
    float / int => float

    int / long => long
    long / int => long

    long / float => long
    float / long => long

I have a bad feeling about raising an exception on int division, but I
really
can't say what is so bad about it... maybe that it seems messy.  Division of
a numeric value should yield some kind of numeric value, except in the case
of division by zero, etc.  I really don't think a newbie will appreciate

    >>> 1 / 2
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    IntDivisionError: integer division is invalid

any more than they currently understand

    >>> 1 / 2
    0