[ColinWright]

You're using python3. My brief experiments showed it actually ran faster in python2. You might want to re-run your experiments to see if I've done anything stupid with that test.

But definitely it seemed that python2 and python3 had significantly different performance.

[Ysx]

Oh you're right, that's interesting - have replicated your result.

"a2 = a2+c; c = c+2" is still fastest on both 2 and 3, though don't know enough to say why.

[joshuamorton]

Try python 3.7, iirc it should be faster again