how to get bit info

[Stephen Hansen]

On 6/17/10 1:29 PM, Grant Edwards wrote:
> On 2010-06-17, Stephen Hansen <me+list/python at ixokai.io> wrote:
> 
>>>>> BIT_1 = 1 << 0
>>>>> BIT_2 = 1 << 1
> 
> ...
> 
>> Basically, those BIT_X lines are creating numbers which have *only* the
>> specified bit set. Then you do "byte & BIT_X", and that will return 0 if
>> the byte doesn't have the specified bit in it. You can then set the bit
>> with "byte | BIT_X", and unset the bit with "byte ^ BIT_X".
> 
> Just to clarify, "byte ^ BIT_X" inverts (toggles) bit X.
> 
> If you want to make sure bit X is a 0 (which is what people usually
> mean by "unset"), you do "byte & ~BIT_X"

Doh, you're correct. I got so used to the pattern of only ever flipping
the bit off after for some reason I knew it was on, like:

if blah & CONSTANT_A:
   do-stuff
   blah = blah ^ CONSTANT_A

That I forgot ^ was invert >_>

Ahem! Thanks for the correction.

-- 

   Stephen Hansen
   ... Also: Ixokai
   ... Mail: me+list/python (AT) ixokai (DOT) io
   ... Blog: http://meh.ixokai.io/

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