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According to the pypy people, the type annotations also don't provide the kind of information the JIT wants. The JIT cares about things like "this integer fits into a machine word" and "this parameter can be None but is almost always not None" so on. The type system doesn't concern itself with that.

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It’s definitely true that there’s stuff a JIT would love to know that the type system can’t tell you. But that doesn’t mean there isn’t useful information available in type annotations. In particular it is possible to speed up attribute access and method/function calls a lot when target types are statically known.

Our approach to “int fits in a machine word” in Static Python is to require machine ints to be explicitly annotated as such, and then you opt in to limited size ints with overflow etc, in exchange for getting really fast arithmetic.

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