On Thu, 2006-11-16 at 08:09 -0800, Danny Colligan wrote: > > The more trivial the example, the harder it is to see the advantage. > > I absoultely agree. Thanks for pointing me out to some real-world > code. However, the function you pointed me to is not a generator > (there is no yield statement... it just returns the entire list of > primes). A generator version would be: > > >>> def primes(n): > ... if n<2: yield [] > ... s=range(3,n+1,2) > ... mroot = n ** 0.5 > ... half=(n+1)/2-1 > ... i=0 > ... m=3 > ... while m <= mroot: > ... if s[i]: > ... j=(m*m-3)/2 > ... s[j]=0 > ... while j<half: > ... s[j]=0 > ... j+=m > ... i=i+1 > ... m=2*i+3 > ... yield 2 > ... for x in s: > ... if x: yield x
Not quite: >>> x = primes(1) >>> x.next() [] >>> x.next() 2 >>> x.next() Traceback (most recent call last): File "<stdin>", line 1, in ? StopIteration To handle n<2 correctly, you have to "return" instead of "yield []". >>> x = primes(1) >>> x.next() Traceback (most recent call last): File "<stdin>", line 1, in ? StopIteration -Carsten -- http://mail.python.org/mailman/listinfo/python-list
