[Tutor] working with bit arrays

[Robert Berman]

Wayne,

Thank you very much.

Robert

On Wed, 2009-12-02 at 12:48 -0600, Wayne Werner wrote:
> On Wed, Dec 2, 2009 at 12:08 PM, Robert Berman <bermanrl at cfl.rr.com>
> wrote:
> 
>         Hi,
>         
>         I am trying to represent a number as a list of bits: for
>         example the bit representation of the integer 8. I did find a
>         number of articles pertaining to a module called bitarray but
>         I was unable to download/install that package. I am using
>         Linux on Ubuntu 9.10; Python 2.6.2. 
>         
>         I am almost certain there is a relatively easy way to convert
>         an integer that can be represented by 32 bits into an array of
>         bits that I can iterate over looking for switched on bits or
>         switched off bits. 
>         
>         Any information such as recipes or past articles in this list
>         providing methods to create and manipulate  bit arrays would
>         be most appreciated.
>         
> 
> 
> Python 2.6+ (as far as I know) has the bin() function:
> 
> 
> Python 2.6.2 (r262:71605, Apr 14 2009, 22:40:02) [MSC v.1500 32 bit
> (Intel)] on
> win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> bin(8)
> '0b1000'
> >>>
> 
> 
> And larger:
> 
> 
> >>> bin(99999999999999999999999)
> '0b10101001011010000001011000111111000010100101011110110011111111111111111111111'
> 
> 
> You can convert them to integers to use ^ (XOR) or & (AND) and other
> binary operations on
> them: http://docs.python.org/reference/expressions.html#binary-bitwise-operations
> 
> 
> >>> a = int('01001', 2)
> >>> b = int('00001', 2)
> >>> a & b == b
> True
> >>> a = int('01110', 2)
> >>> a & b == b
> False
> 
> 
> There may be some other way to check, but that's probably the easiest
> I know of.
> 
> 
> HTH,
> Wayne
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