It seems like there are a couple topics that come up when talking to people about switching to PyPy: - performance or memory usage on larger programs - C extens

It seems like there are a couple topics that come up when talking to people about switching to PyPy: - performance or memory usage on larger programs - C extension module support I'm not going to promise that we will do a better job at these, but there are technical reasons to think that it's possible. You're definitely right, Python has a lot of user-customizability that can make it harder to execute efficiently than JavaScript (though thankfully it has less than Ruby). Both PyPy and Pyston have their techniques for cutting through the complicated+expensive slow case and trying to predict and execute a fast path.