Python math is off by .000000000000045
Christian Heimes
lists at cheimes.de
Wed Feb 22 19:26:26 CET 2012
Am 22.02.2012 19:13, schrieb Alec Taylor:
> Simple mathematical problem, + and - only:
>
>>>> 1800.00-1041.00-555.74+530.74-794.95
> -60.950000000000045
>
> That's wrong.
That's only the correct answer for unlimited precision, not for IEEE-754
semantics. http://en.wikipedia.org/wiki/IEEE_754
> Proof
> http://www.wolframalpha.com/input/?i=1800.00-1041.00-555.74%2B530.74-794.95
> -60.95 aka (-(1219/20))
>
> Is there a reason Python math is only approximated? - Or is this a bug?
Python uses the platforms double precision float datatype. Floats are
almost never exact.
Christian
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