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Date: Tue, 15 Apr 2014 19:31:36 +0100
From: Phil Dobbin <phildobbin@gmail.com>
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Subject: Re: Simple question
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Xref: csiph.com comp.lang.python:70282

On 15/04/2014 19:25, Zachary Ware wrote:

> On Tue, Apr 15, 2014 at 1:18 PM, Phil Dobbin <phildobbin@gmail.com> 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?
> 
> First, note that the "..." part of "5.55111..." is very important
> here, it's actually "5.55111...e-17" which means it's really
> approximately 0.000000000000000055111, which is really very close to
> the answer you'd expect from a human.  To learn more about why Python
> doesn't give 0.0, read this:
> https://docs.python.org/3/tutorial/floatingpoint.html
> 
> Hope this helps,
> 

Hi, Zach.

I saw the 'e-17' appended to the end but was unsure of its meaning (
quite a number of things are introduced in the book with clarification
of their meaning not forthcoming 'til later on).

Thank you for the link. It'll be very helpful.

Cheers,

  Phil...

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