I'm trying to make a lazy, (theoretically) infinite prime number sieve
using generators. The code I have thus far is:
#!/usr/bin/env python
import itertools
def sieve():
nats = naturals(2)
while True:
elem = nats.next()
yield elem
nats = itertools.ifilterfalse(lambda x: x % elem == 0, nats)
def naturals(start=1):
curr = start
while True:
yield curr
curr += 1
primes = sieve()
i = 0
while i < 10:
print primes.next()
i += 1
When I execute this code, the numbers 2,3,4,...,11 are printed (i.e.
nothing gets filtered out). Could anyone explain why this is
happening? I generally understand generators, and my hypothesis is
that reassigning to nats the result of filtering nats could be
screwing things up somehow, but I've tried a variety of other methods,
from making copies of the old iterator to rolling my own filter
function and nothing has worked.
Thanks,
-MRH
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