How to Read Bytes from a file

[Leif K-Brooks]

Alex Martelli wrote:
> You should probaby prepare before the loop a mapping from char to number
> of 1 bits in that char:
> 
> m = {}
> for c in range(256):
>   m[c] = countones(c)

Wouldn't a list be more efficient?

m = [countones(c) for c in xrange(256)]