[Python-Dev] Decimal <-> float comparisons in py3k. (original) (raw)

Steven D'Aprano steve at pearwood.info
Thu Mar 18 20:34:19 CET 2010

On Fri, 19 Mar 2010 05:27:06 am Glenn Linderman wrote:

> Do you envisage any problems from allowing this instead? > >>>> Decimal('1.1')< 2.2_ _> > True

Yes. As any non-naïve float user is aware, the proper form of float comparisons is not to use < or > or == or !=, but rather, instead of using < (to follow along with your example), one should use: Decimal('1.1') - 2.2 < epsilon

And yet we allow

1.1 < 2.2

instead of forcing users to do the "proper form". One can only wonder why the various standards (actual and de-facto) for floating point allows comparisons at all.

But they do, and so does Python, and frankly even if the only reason is to satisfy lazy coders who don't have a requirement for high accuracy, then that's a good reason in my book, and one equally applicable to Decimal and float.

-- Steven D'Aprano

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