[Python-Dev] Deprecating float.is_integer()

[Devin Jeanpierre]

> [Mark Dickinson <dickinsm at gmail.com> ]
>> If you have a moment to share it, I'd be interested to know what value of
>> `x` you used to achieve this, and what system you were on. This can't happen
>> under IEEE 754 arithmetic.
>
> I expect it might happen under one of the directed rounding modes
> (like "to +infinity").

PyPy (5.8):

>>>> x = 1e300
>>>> x.is_integer()
True
>>>> math.sqrt(x**2).is_integer()
False
>>>> x**2
inf

(It gives an OverflowError on my CPython installs.)

I believe this is allowed, and Python is not required to raise
OverflowError here:
https://docs.python.org/3.6/library/exceptions.html#OverflowError
says:

> for historical reasons, OverflowError is sometimes raised for integers that are outside a required range. Because of the lack of standardization of floating point exception handling in C, most floating point operations are not checked

-- Devin