[Numpy-discussion] CASTABLE flag

[Charles R Harris]

Hi,

On Jan 7, 2008 1:16 PM, Timothy Hochberg <tim.hochberg at ieee.org> wrote:

>
> Another possible approach is to treat downcasting similar to underflow.
> That is give it it's own flag in the errstate and people can set it to
> ignore, warn or raise on downcasting as desired. One could potentially have
> two flags, one for downcasting across kinds (float->int, int->bool) and one
> for downcasting within kinds (float64->float32). In this case, I personally
> would set the first to raise and the second to ignore and would suggest that
> as the default.
>
> IMO:
>
>    1. It's a no brainer to raise and exception when assigning a complex
>    value to a float or integer target. Using "Z.real" or "Z.imag" is
>    clearer and has the same performance.
>    2. I'm fairly dubious about assigning float to ints as is. First off
>    it looks like a bug magnet to me due to accidentally assigning a floating
>    point value to a target that one believes to be float but is in fact
>    integer. Second, C-style rounding is pretty evil; it's not always consistent
>    across platforms, so relying on it for anything other than truncating
>    already integral values is asking for trouble.
>    3. Downcasting within kinds seems much less hazardous than
>    downcasting across kinds, although I'd still be happy to be able regulate it
>    with errstate.
>
> Maybe a combination of a typecast function and the errstate would work
well. The typecast function would provide a clear local override of the
default errstate flags, while the user would have the option to specify what
sort of behavior they care about in general.

Chuck
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