Floating point weirdness

[Benjamin Niemann]

Joshua Ginsberg wrote:

> WTF, mate?
> 
> 
>>>>import sys
>>>>sys.version
> 
> '2.3.3 (#1, May  7 2004, 10:31:40) \n[GCC 3.3.3 20040412 (Red Hat Linux
> 3.3.3-7)]'
> 
>>>>float('19.95')
> 
> 19.949999999999999
> 
>>>>round(19.94999999999999999, 2)
> 
> 19.949999999999999
> 
>>>>round(19.949, 1)
> 
> 19.899999999999999
> 
> Why can't I just get 19.95?
floats are represented as 64 (or 128?) bit values and there's no value 
that exactly represents 19.95 or 19.9 (=round(19.949, 1)). The last 
example results in the closest value to 19.9, but not exactly. Python 
prints this value with maximum precision. If you want a string 
representation of a float with e.g. 2 digits precision, use
"%.2f" % 19.949