Why is Python slow (2016)

The gist of it is:

* Python spends almost all of its time in the C runtime

This means that it doesn't really matter how quickly you execute the "Python" part of Python. Another way of saying this is that Python opcodes are very complex, and the cost of executing them dwarfs the cost of dispatching them. Another analogy I give is that executing Python is more similar to rendering HTML than it is to executing JS -- it's more of a description of what the runtime should do rather than an explicit step-by-step account of how to do it.

Pyston's performance improvements come from speeding up the C code, not the Python code. When people say "why doesn't Pyston use [insert favorite JIT technique here]", my question is whether that technique would help speed up C code. I think this is the most fundamental misconception about Python performance: we spend our energy trying to JIT C code, not Python code. This is also why I am not very interested in running Python on pre-existing VMs, since that will only exacerbate the problem in order to fix something that isn't really broken.