python2.4 generator expression > python2.3 list expression

[Peter Otten]

snacktime wrote:

> I need to convert a generator expression to a list expression so it
> will work under python 2.3.
> 
> I rewrote this:
> 
> for c in range(128):
>   even_odd = (sum(bool(c & 1<<b) for b in range(8))) & 1
> 
> As this:
> 
> for c in range(128):
>   bo = [bool(c & 1<<b) for b in range(8)]
>   even_odd = sum(bo) & 1
> 
> 
> Seems to work, is there a better way to do this?

Summing over zeros seems pointless, so

>>> for c in range(128):
...     print len([1 for b in range(8) if c & 1 << b]) & 1,
...
0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1
1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0
1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0
0 1 0 1 1 0 0 1 1 0 1 0 0 1

The same simplification works for genexps, but you have to use sum() there
instead of len(). Another optimization would be to precalculate the
bitmasks [1 << b for b in range(8)] outside the loop.

Peter