Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #20691 > unrolled thread

Re: Python math is off by .000000000000045

Back to article view | Back to comp.lang.python

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: Python math is off by .000000000000045 Christian Heimes <lists@cheimes.de> - 2012-02-22 19:26 +0100
    Re: Python math is off by .000000000000045 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-22 22:21 +0000

#20691 — Re: Python math is off by .000000000000045

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

[toc] | [next] | [standalone]

#20698

On Wed, 22 Feb 2012 19:26:26 +0100, Christian Heimes wrote:

> Python uses the platforms double precision float datatype. Floats are
> almost never exact.

Well, that's not quite true. Python floats are always exact. They just 
may not be exactly what you want :)

Pedantic-but-unhelpful-as-always-ly y'rs,


-- 
Steven

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web