Class instantiation slower in Python 3 than Python 2

Question

I noticed by chance that a simple program generating a class from a large datafile ran a lot faster in Python 2.7 vs. 3.5. I read here that the use of "infinite precision" integers was to blame for slowdown in simple enumeration, but even when I tried a simple test instantiating this class I found that Python 3 was significantly slower:

class Benchmark(object):
    def __init__(self):
        self.members = ['a', 'b', 'c', 'd']


def test():
    test = Benchmark()

if __name__ == '__main__':
    import timeit
    print(timeit.timeit("test()", setup="from __main__ import test"))

I thought perhaps it was something to do with the size of each class instance, but the Python 3 instance was smaller than 2 (56 vs. 64)

$python3 benchmarks.py
0.7017288669958361
$python benchmarks.py
0.508942842484

I have tried many variations on this theme, including with 3.4 on a different machine, and still get the same results. Any ideas what's going on?

Answer 1

You are not measuring class instantiation time, you are measuring class instantiation, plus assignment, plus list creation, ...

Here's a correct benchmark:

$ python -m timeit -s 'class C(object): pass' 'C()'
10000000 loops, best of 3: 0.0639 usec per loop
$ python3 -m timeit -s 'class C(object): pass' 'C()'
10000000 loops, best of 3: 0.0622 usec per loop

As you can see, Python 3 is sightly faster.