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

Glenn Linderman v+python at g.nevcal.com
Wed Mar 24 23:09:29 CET 2010

On 3/24/2010 1:56 PM, Raymond Hettinger wrote:

FWIW, my viewpoint on this is softening over time and I no longer feel a need to push for a new context flag.

To make Decimal useful for people that want to control its numerical quality, there must be a way to exclude accidental operations, and preferably an option for producing exceptions. Otherwise the status quo in 3.x is preferable to adding it to the numeric tree.

I agree that not worrying can make you feel better, though. :)

IIRC, the original purpose of a NaN was to serve as a placeholder value in a long series of floating point ops so that the programmer would not have to introduce edge case tests at each stage of a calculation. Yet, I look at the code for the decimal module and the C code for the math module and see that the opposite result occurred, the code is littered with isspecial(x) tests and handlers.

You are looking at the wrong code. The point is that the code using the math module and decimal module doesn't have to be littered with edge case tests; not that the implementation, which the good folks at IEEE figured would be in custom silicon that could do the edge case checking in parallel with other operations and with no net slowdown, would not have to be littered with edge cases.

Glenn

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