Euler Problem #2: Fibonacci Numbers

fibonacci() is from Diving Into Python by Mark Pilgrim

>>> def fibonacci():
... a,b = 0,1
... while a <= 4000000:
... yield a
... a,b = b, a + b
...
>>> total = 0
>>> for n in fibonacci():
... if n%2 == 0:
... total += n
...
>>> print total
4613732