genexp performance problem?

[Kent Johnson]

Delaney, Timothy (Tim) wrote:
> python -mtimeit "sum(int(L) for L in xrange(3000))"
> 100 loops, best of 3: 6.76 msec per loop
> 
> python -mtimeit -s "g = (int(L) for L in xrange(3000))" "sum(g)"
> 1000000 loops, best of 3: 1.09 usec per loop
> 
> The generator comprehension needs to create a new generator each time
> around.

Reusing the generator doesn't give a correct answer; after the first 
sum() the generator is exhausted:

In [1]: g=(int(L) for L in xrange(10))

In [2]: sum(g)
Out[2]: 45

In [3]: sum(g)
Out[3]: 0

Kent