python2.4 generator expression > python2.3 list expression

[Duncan Booth]

Bryan wrote:

>> is to reset the rightmost (less significant) '1' bit of a number (ie
>> change it to '0').
> 
> i tried c &= c - 1 but i'm not getting the least significant or
> rightmost bit reset to zero.  am i misunderstanding something?
> 
> >>> 2 & 1  # 2 = 0x10; reset right most would be 0x10
> 0
> >>> 10 & 9 # 10 = 0x1010; reset right most would be 0x1010
> 8

The difference between the original "reset the rightmost '1' bit", and your 
interpretation: "reset the rightmost bit" is the "'1'".

The rightmost bit that is set is reset. So 0x10 -> 0, and 0x1010 -> 0x1000.

If you want to extract the least significant set bit from a number 'x' you 
can use (x&-x):

>>> x = 0xab4
>>> while x:
	print hex(x&-x), hex(x)
	x ^= (x&-x)

	
0x4 0xab4
0x10 0xab0
0x20 0xaa0
0x80 0xa80
0x200 0xa00
0x800 0x800
>>> 

(but don't try this if x is negative: it works but never terminates).