PyPy won't be a candidate in some scenarios (nor is it always that much faster), and even libraries written in C leave some performance on the table when Python

PyPy won't be a candidate in some scenarios (nor is it always that much faster), and even libraries written in C leave some performance on the table when Python is the glue language. Don't get me wrong, I'm hardly ever in a position where Python limits me from a performance perspective ... there's always Cython. But it could be better.