Determining combination of bits

[Peter Abel]

"Sean Berry" <sean at buildingonline.com> wrote in message news:<x3Qjd.121786$hj.41260 at fed1read07>...
> Say I have a dictionary like the following
> 
> {1:'one',2:'two',4:'three',8:'four',16:'five', etc...}

Dont know exactly what your dictionary should represent.
Since 2**0 = 1
      2**1 = 2
      2**2 = 4
      etc.
So I would have expected something like:
{1:'zero',2:'one',4:'two',8:'three',16:'four',32:'five', etc...}


> 
> and I am given some numbers, say 22, 25, and 9.  I want to determine the 
> keys, powers of 2, that comprise the number.
> 
> Ex.  22 = 16+4+2
>        25 = 16+8+1
>        9   = 8+1
> ...etc...
> 
> How do I get these keys?

Solution No. XXXXXXXX:

>> def fn(n):
... 	number=n
... 	if n<=0:
... 		return 'n must be greater 0'
... 	keys=[]
... 	i=1
... 	while n:
... 		if n&1:
... 			keys.append(i)
... 		n=n>>1
... 		i*=2
... 	keys.reverse()
... 	l=map(str,keys)
... 	print '%d = %s' % (number,'+'.join(l))
... 	return keys
... 
>>> print fn(22)
22 = 16+4+2
[16, 4, 2]
>>> print fn(25)
25 = 16+8+1
[16, 8, 1]
>>> print fn(255)
255 = 128+64+32+16+8+4+2+1
[128, 64, 32, 16, 8, 4, 2, 1]
>>> 

Sorry I have only Python 2.2. and though I'm a one-liner-fan my
solution should be clear.

Regards Peter