Not the perfect benchmark but

```
$python --version
Python 3.4.2
$ python -m timeit 'print("foo" + str(3.14) + "bar")'
100000 loops, best of 3: 16.4 usec per loop
$ python -m timeit 'print("foo{}bar".format(3.14))'
100000 loops, best of 3: 19.2 usec per loop

```