Binary Decimals in Python

Tue Mar 30 16:19:33 EDT 2010

Chris
On Tue, Mar 30, 2010 at 11:14 AM, John Nagle <nagle at animats.com> wrote:
> aditya wrote:
>>> On Mar 30, 10:49 am, Raymond Hettinger <pyt... at rcn.com> wrote:
>>>>> On Mar 30, 8:13 am, aditya <bluemangrou... at gmail.com> wrote:
>>>>>> To get the decimal representation of a binary number, I can just do
>>>> this:
>>>> int('11',2) # returns 3
>>>> But decimal binary numbers throw a ValueError:
>>>> int('1.1',2) # should return 1.5, throws error instead.
>>>> Is this by design? It seems to me that this is not the correct
>>>> behavior.
>>>>>>> The int() constructor returns integers.
>>> So, look to float() for non-integral values.
>>> Binary representation isn't supported yet,
>>> but we do have hex:
>>>>>> >>> float.fromhex('1.8')
>>> 1.5
>>>>>> Raymond
>>>>>>> That looks very elegant, thanks!
>>>> Hex floats are useful because you can get a string representation
> of the exact value of a binary floating point number. It should
> always be the case that
>> float.fromhex(float.hex(x)) == x
>> That's not always true of decimal representations, due to rounding
> problems.
>
Actually, any number you can represent exactly in base 2 (or any power there
of) you can also represent exactly in decimal - its the other way around
thats a problem.
>> Long discussion of this here: "http://bugs.python.org/issue1580"
>>> John Nagle
>>>>> --
> http://mail.python.org/mailman/listinfo/python-list
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