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by mixmastamyk 1356 days ago
No such thing as a constant in Python. You can optionally name a variable in uppercase to signal to others that it should be, but that's about it.

You can write a new compiler if you'd like, as detailed on this page. But CPython doesn't work that way and 99% of the ecosystem is targeted there.

There is some work on making more assumptions as it runs, now that the project has funding. This is about where my off-top-of-head knowledge ends however so someone else will want to chime in here. The HN search probably has a few blog posts and discussions as well.
1 comments
chrisseaton 1356 days ago
> No such thing as a constant in Python. You can optionally name a variable in uppercase to signal to others that it should be, but that's about it.

Yeah that’s the point - the JIT takes that capitalisation as a hint to treat it as a true constant and bake the value in until it’s redefined.

This is all solved stuff and isn’t a barrier to implementing a powerful JIT for Python if someone wanted to.

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mixmastamyk 1356 days ago
It's solved stuff in languages other than Python. Many groups even at google have tried and failed.
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chrisseaton 1356 days ago
No, we know how to optimise all these issues. They're solved, through a combination of online profiling, inline caching, splitting, deoptimisation, scalar replacement, etc. (I wrote a PhD on it.) I don't think you could name a single Python language feature that we don't know how to optimise efficiently. (I'd be interested if you could.) But implementing them all is a difficult engineering challenge, even for Google, mainly because it involves storing a lot of state in a system that isn't designed to have state attached everywhere.
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mixmastamyk 1355 days ago
Yes, that’s what my reply means, your “no…” is poor communication style. If you think you can do better than the folks working on it for a decade plus, by all means step up.
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chrisseaton 1355 days ago
But you can't actually give any examples? Ok.

I'll give you one you could have used - the GIL - however I'm not sure the GIL's semantics are really specified for Python, they're an implementation detail people accidentally have relied on.

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