Hi, A little bit more on this :)
Python iterator protocol will call the next() method on the iterator on each iteration and receive the values from your iterator until a StopIteration Exception is raised. This is how the for clause knows to iterate. In your example below you can see this with the next example: >>> gen = fibonacci(3) >>> gen.next() 0 >>> gen.next() 1 >>> gen.next() 1 >>> gen.next() 2 >>> gen.next() Traceback (most recent call last): File "<stdin>", line 1, in <module> StopIteration >>> Thanks, Raúl On Wed, Jul 9, 2014 at 4:18 PM, Raúl Cumplido <raulcumpl...@gmail.com> wrote: > Hi, > > Let's see what happens iteration by iteration. First iteration: > > def fibonacci(max): #using a generator >> > a, b = 0, 1 >> > # The value of a is 0 and b is 1, easy :) > >> while a < max: >> > yield a >> > # yield a (0) (yield is a keyword that is used like return but returns a > generator). This value will be sent to the for iteration on the first > iteration. > > On the second iteration: > >> a, b = b, a+b >> > # a is 1 now and b is 1 (1+0) > And then yield a which now is 1 > > On the third iteration: > >> a, b = b, a+b >> > # a is 1 now and b is 2 (1+1) > And then yield a which now is 1 > > On the forth iteration: > >> a, b = b, a+b >> > # a is 2 now and b is 3 (2+1) > And then yield a which now is 2 > > >> for n in fibonacci(1000): >> print n, >> ------ >> > > n is the value for each iteration that the yield statement is returning. > You can read the response on this thread if you want to understand more > about yield, generators and iterators. > > Thanks, > Raúl > -- Raúl Cumplido
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