[Python-Dev] Mixing float and Decimal -- thread reboot (original) (raw)

Guido van Rossum guido at python.org
Wed Mar 24 20:51:13 CET 2010

On Wed, Mar 24, 2010 at 11:55 AM, Alexander Belopolsky <alexander.belopolsky at gmail.com> wrote:

On Wed, Mar 24, 2010 at 2:36 PM, Guido van Rossum <guido at python.org> wrote: ..

Probably because we were blindly following the IEEE standard without understanding it in every detail. Are you talking about "accidental" support for NaNs in older versions of Python or about recent efforts to support them properly in math and decimal modules?

My recollection include recent efforts, such as the math.isnan() function.

I don't recall ever hearing an argument for the peculiar behavior of NaN in comparisons beyond "this is what the IEEE standard prescribes."

I feel you are too harsh on the developers that worked in this area.

Maybe. I didn't mean to put down individuals complicit in the decision -- in fact I would say that I am to blame myself for not probing deeper.

I dare to suggest that the current situation is not due to lack of understanding of the standard, but due to pragmatic decisions made in early development and desire for backward compatibility in the recent versions.

I think that originally NaN (and Inf) behavior was so platform-dependent that it really wouldn't have mattered if we had changed it.

Is this an area where design changes are feasible?  IIRC, NaN support was never "officially" in the language, but it may have changed with the decimal module.

It has been at least since 2.6 introduced math.isnan(), and ISTR there was a proposal to add a separate module to deal with NaN and Inf properly in a pure-python library module.

-- --Guido van Rossum (python.org/~guido)

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