Unlike other range()-like functions random.randrange() accepts not only integers and integer-like objects (implementing __index__), but any numbers with integral values, like 3.0 or Decimal(3). In 3.8 using __int__ for implicit converting to C integers were deprecated, and likely will be forbidden in 3.9. __index__ is now preferable.

I propose to deprecate accepting non-integer arguments in random.randrange() and use __index__ instead of __int__ for converting values. At end it will lead to simpler and faster code. Instead of

        istart = _int(start)
        if istart != start:
            raise ValueError("non-integer arg 1 for randrange()")

we could use just

        start = _index(start)

It will help also in converting the randrange() implementation to C.

See also issue37315.