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by Jtsummers 598 days ago
Common Lisp is probably not a good point of comparison. It offers comparable (if not more) dynamism to Python and still remains fast (for most implementations). You can redefine class definitions and function definitions on the fly in a Common Lisp program and other than the obvious overhead of invoking those things the whole system remains fast.
2 comments
eigenspace 598 days ago
Common lisp is in fact a good point of comparison once you look at how it's fast. The trick with Common Lisp is that they made a foundation of stuff that can actually be optimized pretty well by a compiler, and made that stuff exempt from being changed on the fly (or in some cases, just made the the compiler assume that they won't change on the fly even if they do, resulting in seg-faults unless you recompile code and re-generate data after changing stuff).

This is how Common Lisp people can claim that the language is both performant and flexible. The performant parts and the flexible parts are more disjoint than one might expect based on the way people talk about it.

But anyways, Common Lisp does manage to give a high degree of dynamism and performance to a point that it surely can be used for any of the dynamic stuff you'd want to do in Python, while also giving the possibility of writing high performance code.

Python did not do this, and so it'll be impossible for them to offer something like common lisp perf without breaking changes, or by just introducing a whole new set of alternatives to slow builtins like class, int, call, etc.

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Jtsummers 598 days ago
> > Why does python have to be slow?

> Because the language's semantics promise that a bunch of insane stuff can happen at any time during the running of a program, including but not limited to the fields of classes changing at any time.

You originally claimed Python is slow because of its semantics and then compare later to CL. CL has a very similar degree of dynamism and remains fast. That's what I'm saying makes for a poor comparison.

CL is a demonstration that Python, contrary to your initial claim, doesn't have to forfeit dynamism to become fast.

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lispm 598 days ago
> CL has a very similar degree of dynamism and remains fast.

But not the dynamic parts remain "really" fast. Common Lisp introduced very early a lot of features to support optimizing compilers -> some of those reduce "dynamism". Code inlining (-> inline declarations), file compiler semantics, type declarations, optimization qualities (speed, compilation-speed, space, safety, debug, ...), stack allocation, tail call optimization, type inferencing, ...

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eigenspace 598 days ago
I think you're missing the point. Common Lisp is very dynamic yes, but it was designed in a very careful way to make sure that dynamism does not make an optimizing compiler impossible. That is not the case for Python.

Not all dynamism is the same, even if the end result can feel the same. Python has a particularly difficult brand of dynamism to deal with.

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Archit3ch 597 days ago
> You can redefine class definitions and function definitions on the fly in a Common Lisp program and other than the obvious overhead of invoking those things the whole system remains fast.

You can also treat Julia as C and recompile vtables on the fly.

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