python 3.44 float addition bug?

[Steven D'Aprano]

On Mon, 23 Jun 2014 17:55:50 -0700, buck wrote:

> It used to be that the best way to compare floating point numbers while
> disregarding the inherent epsilon was to use `str(x) == str(y)`. It
> looks like that workaround doesn't work anymore in 3.4.

What inherent epsilon? Can you explain what you mean?


> What's the recommended way to do this now?
> 
>>>> format(.01 + .01 + .01 + .01 + .01 + .01, 'g') == format(.06, 'g')
> True


That's equivalent to doing an implicit round. If all you want to do is 
round your calculations, then explicitly round them:

py> x = sum([0.01]*6)
py> y = 0.06
py> round(x, 12) == round(y, 12)
True

Not that I'm recommending that you do it this way, but an explicit round 
is better than using string formatting.

See also this:

http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/



-- 
Steven