off topic but please forgive me me and answer

David Robinow drobinow at gmail.com
Fri Apr 2 05:08:01 CEST 2010


On Thu, Apr 1, 2010 at 10:44 PM, Steven D'Aprano
<steve at remove-this-cybersource.com.au> wrote:
> On Thu, 01 Apr 2010 19:49:43 -0500, Tim Chase wrote:
>
>> David Robinow wrote:
>>> $ python -c "print 1/2 * 1/2"
>>> 0
>>>
>>>  But that's not what I learned in grade school.
>>> (Maybe I should upgrade to 3.1?)
>>
>> That's because you need to promote one of them to a float so you get a
>> floating-point result:
>>
>>    >>> 1/2 * 1/2
>>    0
>>    >>> 1/2 * 1/2.0
>>    0.0
>>
>> Oh...wait ;-)
>
> Tim, I'm sure you know the answer to this, but for the benefit of the
> Original Poster, the problem is that you need to promote *both* divisions
> to floating point. Otherwise one of them will give int 0, which gives 0.0
> when multiplied by 0.5.
>
>>>> 1.0/2 * 1/2.0
> 0.25
>
>
> If you want an exact result when multiplying arbitrary fractions, you
> need to avoid floats and decimals and use Fractions:
>
>>>> Fraction(1, 2)**2
> Fraction(1, 4)

I should have known he wouldn't get it.



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