[Pythonmac-SIG] round() not consistent?

[israel at uandmedance.com]

Thanks Bob and Calvin

I would have though round() would cut off those extra digits, but I'll 
go and do my freshly assigned homework and educate myself.  :)


Thanks again,

~Israel~


On Friday, May 28, 2004, at 01:47 PM, Bob Ippolito wrote:

>
> On May 28, 2004, at 2:41 PM, israel at uandmedance.com wrote:
>
>>
>> hello everyone..
>>
>> I've been playing around with generating some random numbers with 
>> random.random and then rounding them off to two decimal points with 
>> round() but for some reason this doesn't always work.
>>
>> here is a sample session
>> '''
> ---
>> >>> round(random.random(),2)
>> 0.57999999999999996
> ---
>> Am I just not understanding how things work here?
>
> You are not understanding how things work here.  Floating point 
> numbers can not exactly represent all decimal numbers.  What you are 
> looking at is the __repr__ of the floating point return values, which 
> shows the precise value of what the float actually contains so that it 
> can be used to reconstruct the exact value.
>
> The __str__ of those values would be what you expect to see as a 
> 'human'.  Try str(0.57999999999999996), and you will see '0.58'.
>
> Google for "ieee 754", and you will find all the information you ever 
> wanted to know about floating point numbers (as implemented by typical 
> computers and compilers).  To be more specific, Python's float 
> corresponds to C's double, which is 64bits wide on almost all 
> platforms.
>
> -bob
>
>
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>



~Israel~
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