Lawrence D'Oliveiro <[email protected]_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.
Try this (essentially equivalent to your code):
def f():
print "hello"
return 1
V = tuple( 1 for x in [1,2,3] for l in (f(),) )
How many "hello"s do you see?
Comprehension are not loops spelled backwards. The values in:
whatever for i ... for j ...
are the values produced by the equivalent code:
for i ...
for j ...
whatever
-- Alain.
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