why do I get this behavior from a while loop?

[Diez B. Roggisch]

S. Chris Colbert schrieb:
> This seems strange to me, but perhaps I am just missing something:
> 
> In [12]: t = 0.
> In [13]: time = 10.
> 
> In [14]: while t < time:
>    ....:     print t    
>    ....:     t += 1.    
>    ....:                
>    ....:                
> 0.0                     
> 1.0                     
> 2.0                     
> 3.0                     
> 4.0                     
> 5.0                     
> 6.0                     
> 7.0                     
> 8.0                     
> 9.0                     
> 
> In [15]: t = 0.
> 
> In [16]: time = 10.
> 
> In [17]: while t < time:
>    ....:     print t    
>    ....:     t += 0.1   
>    ....:                
>    ....:                
> 0.0                     
> 0.1                     
> 0.2                     
> 0.3                     
> <--snip-->
> 9.4
> 9.5
> 9.6
> 9.7
> 9.8
> 9.9
> 10.0
> 
> 
> I would think that second loop should terminate at 9.9, no? 
> 
> I am missing something fundamental?


Yes. The lack of precision that floating points suffer from (nothing 
python-specific), and the rounding-behavior of printing them.

 >>> t = 0.
 >>> time = 10.
 >>> while t < time:
...     print repr(t)
...     t += .1
...
0.0
0.10000000000000001
<snip/>
9.8999999999999808
9.9999999999999805
 >>>


Diez