🧩 What it means for a type checker to conform to the typing spec

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This article compares Python type checkers by how closely they follow the formal typing specification.

What stands out

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• 📐 Uses a conformance test suite
• ✅ Measures false positives and false negatives
• ⚖️ Conformance is not the same as developer experience
• 🔍 Inference, performance, and IDE integration also matter

The takeaway is useful: it’s not enough to “work”; it also matters how well the tool follows the language rules.

🪄 Quick explanation

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Think of a spell checker.

It’s not enough that it finds mistakes — it also has to avoid flagging correct text as wrong.

👉 Type checkers work the same way.

More information at the link 👇

Python Type Checker Comparison: Typing Spec Conformance | Pyrefly

Learn what it means to conform to the Python typing spec, why it matters, and the conformance status of each type checker including Pyrefly, …

pyrefly.org ↗