one simple example of yield

Write a generator that returns every arrangement of items such that each is in one or none of two different bags.

Each combination should be given as a tuple of two lists, the first being the items in bag1, and the second being the items in bag2.

def yieldAllCombos(items):
    N = len(items)
    
    for i in xrange(3**N):
        bag1 = []
        bag2 = []
        for j in xrange(N):
            # test bit jth of integer i
            if (i/3**j) % 3 == 1:
                bag1.append(items[j])
            if  (i/3**j) % 3 == 2:
                bag2.append(items[j])
        yield (bag1,bag2)

items = [1,7,3]
k=0
for i in yieldAllCombos(items):
    print i
    k+=1
print k

([], [])
([1], [])
([], [1])
([7], [])
([1, 7], [])
([7], [1])
([], [7])
([1], [7])
([], [1, 7])
([3], [])
([1, 3], [])
([3], [1])
([7, 3], [])
([1, 7, 3], [])
([7, 3], [1])
([3], [7])
([1, 3], [7])
([3], [1, 7])
([], [3])
([1], [3])
([], [1, 3])
([7], [3])
([1, 7], [3])
([7], [1, 3])
([], [7, 3])
([1], [7, 3])
([], [1, 7, 3])
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