Normalizing A Vector

Sat Jul 31 21:41:08 EDT 2010

In message <87sk2zhpcj.fsf at dpt-info.u-strasbg.fr>, Alain Ketterlin wrote:
> Lawrence D'Oliveiro <ldo at geek-central.gen.new_zealand> writes:
>>> V = tuple \
>> (
>> x
>> /
>> l
>> for x in V
>> for l in
>> (math.sqrt(reduce(lambda a, b : a + b, (y * y for y in V),
>> 0)),)
>> )
>> You got the order wrong (it has to be for l ... for x ...)

No, I deliberately put it in that order to ensure that the value for l can 
only ever be evaulated once.
> You're kind of lucky here, because the arglist to tuple() provides a
> scope that hides x and l. Be careful if you ever change tuple(...) to
> [...], because x and l would leak to the outer scope (with python 2.*).

Interesting. However, using “list( ... )” instead of “[ ... ]” also prevents 
the leakage.