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Idea: Simpler and More Expressive Type Annotations

davidism (David Lord) Closed September 22, 2026, 2:33pm 86

PEP 849: More Expressive Type Expressions PEPs

I’m excited to present PEP 849, which adds some new background capabilities to the way type annotations are processed in order to let us use arbitrary expressions while maintaining runtime introspection. Currently, you technically can use arbitrary Python expressions in an annotation, so e.g. even var: f(x) if Something else 1 + 17 wouldn’t raise a compiler error. But if we inspect the annotations dict at runtime, we would only ever see the result of calling f or 18, depending on what Something …

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