a print bug?

[Roel Schroeven]

Summercoolness at gmail.com schreef:
> Steve Holden wrote:
>> You obviously haven't yet passed your floating-point number proficiency
>> test yet. Please restrict yourself to integers until you understand the
>> difficulties that inaccuracies in floating-point can create ;-)
> 
> hm, actually, i understand the limitation of floating point.
> but my real concern is, how come "print" favors one version over the
> other...
> the first version will favor the correct rounding, while the second
> doesn't favor it.  to me, this is biased computing....  i will feel
> happier if the behavior is consistent.  (such as the first line
> printing out as 1.2344999999999) .  if most people favor the behavior
> of line 1, that is, silently rounding off to about the 11th decimal
> places, then why doesn't printing with formatting also use that same
> behavior, which is rounding off to the 11th places first, and then
> round off to whatever the user wants.
> 
>>>>> print 1.2345
> 
>> 1.2345
> 
>>>>> print "%10.3f" % 1.2345
> 
>>      1.234
> 
> but then again, i just realize even if i do a
> 
>>>> round(1.2344999999999999999, 6)
> 
> 1.2344999999999999
> 
> so even if you round it off, it is still represented the same way....
> still, how "print" handles 1.2345 and treating it and printing it as
> 1.2345, i wonder why we don't make the "print with formatting" the same
> behavior, treating it as 1.2345 first and round it off to 1.235

You do realize that your formatting uses less decimal places than the 
print statement, do you?

 >>> print 1.2345
1.2345
 >>> print "%0.3f" % 1.2345
1.234
 >>> print "%0.4f" % 1.2345
1.2345

If you use 4 decimals after the decimal sign, you get the same result as 
with a plain print statement (at least in this case). That means that 
print is not treating it as 1.2345 first and then rounding it off to 
1.235; it is just using the actual internal representation and rounding 
it off to 1.2345. Which IMO is the only sensible thing one can do.


-- 
If I have been able to see further, it was only because I stood
on the shoulders of giants.  -- Isaac Newton

Roel Schroeven