[pjmlp]

Nothing prevents a Python dynamic compiler to follow a similar approach though, specially now that type annotations are part of the language.

And in any case, there are the Smalltalk and SELF JITs as an example of highly dynamic environments, where anything goes.

[kazinator]

With declarations which are promises from the programmer to the compiler (I promise this is true, on penalty of undefined behavior), you can fix a lot of "stupid dynamic".

Python could have a declaration which says, "this function/module doesn't participate in anything stupidly dynamic, like access to parent locals". If it calls some code which tries to access parent locals, the behavior is undefined.

That's kind of a bad thing because in Lisp I don't have to declare anything unsafe to a compiler just to have reasonably efficient local variables that can be optimized away and all that.

[__d]

Type annotations are defined to be completely ignored by the interpreter.

So, as of today, they’re useless for optimization. That could be changed, but hasn’t been so far.