The minimal correction, I guess, is to write
itlist[i] = (x+(i*10) for i in [i] for x in count())
instead of
itlist[i] = (x+(i*10) for x in count())
although
itlist[i] = (x+(i*10) for i,s in (i,count()) for x in s)
will better mimic generalizations in the sense that the "minimal correction"
delays the evaluation of count(), which doesn't matter in the case of count(),
but might make a difference if you replace it with some other expression.
The point is that the first iterator-producing expression in a generator
expression - eg the <X> in (<exp> for vars in <X>...) - is evaluated immediately
in the surrounding context, in contrast to the rest of the genexp.
Cheers, BB
Ken Pu wrote:
Hi, below is the code I thought should create two generates, it[0] =
0,1,2,3,4,5, and it[1] = 0,10,20,30,..., but they turn out to be the
same!!!
from itertools import *
itlist = [0,0]
for i in range(2):
itlist[i] = (x+(i*10) for x in count())
print "what's in the bags:"
print list(islice(itlist[0], 5))
print list(islice(itlist[1], 5))
The output is:
[10, 11, 12, 13, 14]
[10, 11, 12, 13, 14]
I see what Python is doing -- lazy evaluation doesn't evaluate
(x+(i*10) for x in count()) until the end. But is this the right
behaviour? How can I get the output I want:
[0, 1, 2, 3, 4]
[10, 11, 12, 13, 14]
Thanks.
Ken
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