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by ActivePattern 309 days ago
A “sufficiently smart compiler” can’t legally skip Python’s semantics.

In Python, p.x * 2 means dynamic lookup, possible descriptors, big-int overflow checks, etc. A compiler can drop that only if it proves they don’t matter or speculates and adds guards—which is still overhead. That’s why Python is slower on scalar hot loops: not because it’s interpreted, but because its dynamic contract must be honored.
2 comments
pjmlp 309 days ago
In Smalltalk, p x * 2 has that flow that as well, and even worse, lets assume the value returned by p x message selector, does not understand the * message, thus it will break into the debugger, then the developer will add the * message to the object via the code browser, hit save, and exit the debugger with redo, thus ending the execution with success.

Somehow Smalltalk JIT compilers handle it without major issues.

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ActivePattern 309 days ago
Smalltalk JITs make p x * 2 fast by speculating on types and inserting guards, not by skipping semantics. Python JITs do the same (e.g. PyPy), but Python’s dynamic features (like __getattribute__, unbounded ints, C-API hooks) make that harder and costlier to optimize away.

You get real speed in Python by narrowing the semantics (e.g. via NumPy, Numba, or Cython) not by hoping the compiler outsmarts the language.

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afiori 309 days ago
Python'a JIT could do the same, it could check if __getattribute__() is the default implementation and replace its call with p x directly. This would work only for classes that have not been modified at runtime and that do not implement a custom __getattribute__
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pjmlp 309 days ago
People keep forgetting about image based semantics development, debugger, meta-classes, messages like becomes:,...

There is to say everything dynamic that can be used as Python excuse, Smalltalk and Self, have it, and double up.

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tekknolagi 309 days ago
If I may toot my own horn: https://bernsteinbear.com/blog/typed-python/
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cma 309 days ago
edit and continue is available on lots of JIT-runtime languages
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nu11ptr 309 days ago
First, we need to add the word 'only': "not ONLY because it’s interpreted, but because its dynamic contract must be honored." Interpreted languages are slow by design. This isn't bad, it just is a fact.

Second, at most this describes WHY it is slow, not that it isn't, which is my point. Python is slow. Very slow (esp. for computation heavy workloads). And that is okay, because it does what it needs to do.

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