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str more precise in 3 as 2.7

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  str more precise in 3 as 2.7 Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 13:24 +0200
    Re: str more precise in 3 as 2.7 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-04-29 12:50 +0100
    Re: str more precise in 3 as 2.7 Chris Angelico <rosuav@gmail.com> - 2015-04-29 21:55 +1000
      Re: str more precise in 3 as 2.7 Cecil Westerhof <Cecil@decebal.nl> - 2015-04-29 14:09 +0200
    Re: str more precise in 3 as 2.7 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-04-30 14:29 +1000

#89539 — str more precise in 3 as 2.7

I am trying to make my modules also work under Python 3. I found that
str is more precise in Python 3. The expression:
    str(134 / 6.0)
gives in 2.7.8:
    '22.3333333333'
and in 3.4.1:
    '22.333333333333332'

Was not very hard to solve:
    if python_version == 3:
        output06[5] = '22.333333333333332'
        output10[5] = '23.333333333333332'
        output10[8] = '24.77777777777778'

Earlier I did:
    import sys

    # For when the difference between 2 and 3 is important
    python_version = sys.version_info[0]

At the moment I use it only once, but it is never bad to be prepared.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

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#89542

On 29/04/2015 12:24, Cecil Westerhof wrote:
> I am trying to make my modules also work under Python 3. I found that
> str is more precise in Python 3. The expression:
>      str(134 / 6.0)
> gives in 2.7.8:
>      '22.3333333333'
> and in 3.4.1:
>      '22.333333333333332'
>
> Was not very hard to solve:
>      if python_version == 3:
>          output06[5] = '22.333333333333332'
>          output10[5] = '23.333333333333332'
>          output10[8] = '24.77777777777778'
>
> Earlier I did:
>      import sys
>
>      # For when the difference between 2 and 3 is important
>      python_version = sys.version_info[0]
>
> At the moment I use it only once, but it is never bad to be prepared.
>

They simply output different numbers of digits by default.  Just control 
the number of digits that you want to see and in this case you needn't 
worry again about Python 2 vs 3 differences.  See either

https://docs.python.org/3/library/string.html#formatspec

or

https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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#89543

On Wed, Apr 29, 2015 at 9:24 PM, Cecil Westerhof <Cecil@decebal.nl> wrote:
> I am trying to make my modules also work under Python 3. I found that
> str is more precise in Python 3. The expression:
>     str(134 / 6.0)
> gives in 2.7.8:
>     '22.3333333333'
> and in 3.4.1:
>     '22.333333333333332'
>
> Was not very hard to solve:
>     if python_version == 3:
>         output06[5] = '22.333333333333332'
>         output10[5] = '23.333333333333332'
>         output10[8] = '24.77777777777778'

Try using repr() instead of str() - it might be more useful to you.

ChrisA

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#89546

Op Wednesday 29 Apr 2015 13:55 CEST schreef Chris Angelico:

> On Wed, Apr 29, 2015 at 9:24 PM, Cecil Westerhof <Cecil@decebal.nl> wrote:
>> I am trying to make my modules also work under Python 3. I found
>> that str is more precise in Python 3. The expression: str(134 /
>> 6.0) gives in 2.7.8: '22.3333333333' and in 3.4.1:
>> '22.333333333333332'
>>
>> Was not very hard to solve:
>> if python_version == 3:
>> output06[5] = '22.333333333333332'
>> output10[5] = '23.333333333333332'
>> output10[8] = '24.77777777777778'
>
> Try using repr() instead of str() - it might be more useful to you.

That looks very interesting. I am going to use it.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

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#89602

On Wednesday 29 April 2015 21:24, Cecil Westerhof wrote:

> I am trying to make my modules also work under Python 3. I found that
> str is more precise in Python 3. The expression:
>     str(134 / 6.0)
> gives in 2.7.8:
>     '22.3333333333'
> and in 3.4.1:
>     '22.333333333333332'

The precise details of how floats are displayed may vary. In general, if you 
care about the exact details, you should control them by hand using either 
C-style % string interpolation, or the format method:


py> x = 134 / 6.0
py> "%.16f" % x
'22.3333333333333321'
py> "{:.16f}".format(x)
'22.3333333333333321'


-- 
Steve

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