>The single example I typically give is that in Python you can inspect stack frames after they've exited! This has concrete implications on your VM design.

How about an implementation of python that doesn't let you do fancy things like that that are not needed in production?

The inspecting of stack frames is used by the logging library, and by most unit testing libraries. There are dozens of these small features which are challenging, and if you remove all of the challenging ones, you end up with something where pretty much no existing Python can run.

People have tried, pypy started with that goal before it became clear it wasn't practical.

I think logging inspects frames while they're still on the stack, not post-fact..?

Do you happen to know something about the graal python implementation? Based on other comments here, the often used C FFI can also hinder the work of Python implementations, and the graal project solves it by JIT compiling C code as well (from llvm ir)

From what I’ve seen last time I heard about graal python is that it is seldom faster than the pypy approach (AST-based vs tracing JIT), even though in case of TruffleRuby and TruffleJS it is insanely fast compared to the maturity of the projects.

Is your mentioned example of stack frame inspection make it map much worse to Java primitives (which happens behind the scenes of the truffle languages)?

>> in Python you can inspect stack frames after they've exited!

How does that work and what is it used for?

Is there any reason that Python's dynamicness (dynamicity?) is so much more of a hindrance than CL's? Is it just that CL is compiled?

The end of this post explains why Common Lisp can run much faster than Python.

https://markmail.org/message/dp56i26zhpf4fehb#query:+page:1+...

Not more dynamic than Smalltalk or SELF, though.

Please share the well understood criteria for "dynamic" in this context, that would let us order different programming languages as more dynamic or less dynamic.

Search the web for Ruby or Smalltalk or Objective-C “object model” or “message dispatch”

Please share your criteria for "dynamic", that would let us order different programming languages as more dynamic or less dynamic.

Or dylan or julia

Unlike JavaScript however, Python is strongly typed.

Yeah but in practice basically all JS code in the wild is strongly typed since the community has long since decided that relying on implicit type coercion is a massive footgun.

Also I think Python’s truthy/falsey semantics make it dangerously close to being weakly typed.

All that means is that you get more exceptions raised when you use ==. It doesn't help performance at all, it doesn't even really confer anything about types, only that __eq__ is implemented between fewer types.

Python exceptions are low-cost. It has to be that way because every for loop in Python throws an exception.

Python's type system is not more strongly typed than JavaScript's in any way that makes it easier to optimise.