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From: Robert Kern <robert.kern@gmail.com>
Subject: Re: Simple question
Date: Tue, 15 Apr 2014 19:30:36 +0100
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Xref: csiph.com comp.lang.python:70281

On 2014-04-15 19:18, Phil Dobbin wrote:
> Hi, all.
>
> I've just started to learn Python (I'm reading Mark Lutz's 'Learning
> Python' from O'Reilly) & I'm confused as to this part:
>
> '>>> 0.1 + 0.1 + 0.1 - 0.3
> 5.55111.....'
>
> Using 'import Decimal' you can get a much closer result i.e.
> 'Decimal('0.0')'
>
> What I'm wondering is why the first calculation that arrives at
> '5.55111...' is so far out?

The `...` elides the exponent:

   >>> 0.1 + 0.1 + 0.1 - 0.3
   5.551115123125783e-17

If you copied that verbatim directly out of a book, that's just sloppy editing.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco