Pyrefly: Meta's New Python Type Checker is Absurdly Fast | Coding

Meta just open-sourced Pyrefly — a Python type checker so fast it checks 1.85 million lines of code per second. It's already used at Instagram, PyTorch, JAX, NumPy, and Pandas. In this video, I break down what Pyrefly is, why Meta rewrote their entire type checker in Rust, how to set it up in under a minute, and what happens when you run it on a real-world repo. If you write Python — even casually — this tool will change how you catch bugs. ⏱️ CHAPTERS 0:00 Why Python needs a type checker 1:00 Intro to Pyerfly 1:15 The story behind Pyrefly 2:20 GitHub tour 3:10 Installation 4:00 Running Pyrefly on a real repo 6:10 Should you switch? 6:35 Outro 🔗 LINKS - Pyrefly website: https://pyrefly.org - GitHub repo: https://github.com/facebook/pyrefly - Try it in your browser (no install): https://pyrefly.org/sandbox - Meta's announcement: https://engineering.fb.com/2025/05/15/developer-tools/introducing-pyrefly/ 📦 INSTALL pip install pyrefly pyrefly init pyrefly check 💬 QUESTIONS / FEEDBACK Drop a comment with what Pyrefly found in YOUR codebase — I read every one. 🔔 Subscribe: https://www.youtube.com/@AIWithManvinder 💼 LinkedIn: https://www.linkedin.com/in/manvinderchahar #Pyrefly #Python #Meta #TypeChecking #PythonTutorial #python #ai #aiprojects #AIAgents #OpenSource #ArtificialIntelligence #pythonforbeginners #OpenAI #MachineLearning #Tech #Finance #GitHub #Coding #Project #Claude