# A dumb question about a class

Dick Moores rdm at rcblue.com
Mon Aug 13 00:30:02 CEST 2007

At 03:09 PM 8/12/2007, Steven Bethard wrote:

>Here's how I'd write the recipe::
>
>      import itertools
>
>      def iter_primes():
>          # an iterator of all numbers between 2 and +infinity
>          numbers = itertools.count(2)
>
>          # generate primes forever
>          while True:
>
>              # get the first number from the iterator (always a prime)
>              prime = numbers.next()
>              yield prime
>
>              # remove all numbers from the (infinite) iterator that are
>              # divisible by the prime we just generated
>              numbers = itertools.ifilter(prime.__rmod__, numbers)
>
>
>      class PrimeList(object):
>          def __init__(self):
>              # infinite iterator of primes
>              self._prime_iter = iter_primes()
>
>              # the last prime we've seen
>              self._last_prime = None
>
>              # all primes seen so far
>              self._prime_set = set()
>
>              # add the first prime (so that _last_prime is set)
>
>          def __contains__(self, n):
>              # add primes to the list until we exceed n
>              while n > self._last_prime:
>
>              # return True if n is one of our primes
>              return n in self._prime_set
>
>              # take a prime off the iterator and update the prime set
>              self._last_prime = self._prime_iter.next()

I'm afraid my next question is "How do I run this"?

Dick