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) > self._add_prime() > > def __contains__(self, n): > # add primes to the list until we exceed n > while n > self._last_prime: > self._add_prime() > > # return True if n is one of our primes > return n in self._prime_set > > def _add_prime(self): > # take a prime off the iterator and update the prime set > self._last_prime = self._prime_iter.next() > self._prime_set.add(self._last_prime)
I'm afraid my next question is "How do I run this"? Dick -- http://mail.python.org/mailman/listinfo/python-list
