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iterating bit-by-bit across int?

Brian Kelley bkelley at wi.mit.edu
Thu Oct 23 16:07:32 EDT 2003 
Paul Rubin wrote:
> Matthew Wilson <mwilson at sarcastic-horse.com> writes:
> 
>>I'm playing around with genetic algorithms and I want to write a
>>function that mutates an integer by iterating across the bits, and about
>>1 in 10 times, it should switch a zero to a one, or a one to a zero.
>>
>>I'm not sure how many bits are inside a python integer.  The library
>>reference says at least 32.
> 
> 
> Long ints can have as many bits as you want.

Such as -1L which has an infinite number of bits.

I have used a list of integers as my defacto standard for representing a 
stream of bits.  On my windows box this is slower than using a long 
integer but with psyco running (psyco.sourceforge.net) it is faster than 
the long integer implementation.

It also is faster to bail out on a comparison, for example

if (a&b)!= 0:

can be optimized to fail on the first integer failure, it doesn't have 
to complete the operation as it would with a long integer.

This is useful when seeing if a bit string is contained inside another 
bit string.
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