I'm by no means an expert on JIT compilation, but I can give a less technical answer. I think the primary reason is that most of the developers (both CPython c

I'm by no means an expert on JIT compilation, but I can give a less technical answer. I think the primary reason is that most of the developers (both CPython core developers and Python developers) do not consider Python as a tool for writing perfomance critical software. So, any JIT initiative, which requires a lot of resources, doesn't get enough of them. CPython allows to write C extension modules quite easily, so if you need to write some perfomance critical piece of code , you just switch to C and call a C function from Python. Unladen Swallow was a version of CPython that added JIT support. PEP-3146 describes an unsuccessful attempt to merge it into CPython [1]. Here's a postmortem [2] Starting with version 3.6, CPython allows to set a custom frame evaluation function on the interpreter and to store JIT compiled code in a code object. This was done to support JIT in a form of a separate module and is described in PEP 523 [3]. This is very interesting topic. I should study it in detail and probably write a post. I hope I'll be able to give a more thorough answer someday. [1] https://www.python.org/dev/peps/pep-3146 https://www.python.org/dev/peps/pep-3146 [2] http://qinsb.blogspot.com/2011/03/unladen-swallow-retrospective.html http://qinsb.blogspot.com/2011/03/unladen-swallow-retrospect... [3] https://www.python.org/dev/peps/pep-0523/ https://www.python.org/dev/peps/pep-0523/