In [6]: i = 4

In [7]: timeit "Fizz" * (i % 3 == 0)
10000000 loops, best of 3: 118 ns per loop

In [8]: timeit "Fizz" if i % 3 == 0 else ""
10000000 loops, best of 3: 72 ns per loop

In [9]: i = 3

In [10]: timeit "Fizz" * (i % 3 == 0)
10000000 loops, best of 3: 110 ns per loop

In [11]: timeit "Fizz" if i % 3 == 0 else ""
10000000 loops, best of 3: 72.2 ns per loop