Talk Python to Me: #523: Pyrefly: Fast, IDE-friendly typing for Python

Python typing got fast enough to feel invisible. Pyrefly is a new, open source type checker and IDE language server from Meta, written in Rust, with a focus on instant feedback and real-world DX. Today, we will dig into what it is, why it exists, and how it plays with the rest of the typing ecosystem. We have Abby Mitchell, Danny Yang, and Kyle Into from Pyrefly here to dive into the project.<br/> <br/> <strong>Episode sponsors</strong><br/> <br/> <a href='https://talkpython.fm/sentry'>Sentry Error Monitoring, Code TALKPYTHON</a><br> <a href='https://talkpython.fm/agntcy'>Agntcy</a><br> <a href='https://talkpython.fm/training'>Talk Python Courses</a><br/> <br/> <h2 class="links-heading mb-4">Links from the show</h2> <div><strong>Abby Mitchell</strong>: <a href="https://www.linkedin.com/in/abby-mitchell/?featured_on=talkpython" target="_blank" >linkedin.com</a><br/> <strong>Danny Yang</strong>: <a href="https://www.linkedin.com/in/yangdanny97/?featured_on=talkpython" target="_blank" >linkedin.com</a><br/> <strong>Kyle Into</strong>: <a href="https://www.linkedin.com/in/kyleinto/?featured_on=talkpython" target="_blank" >linkedin.com</a><br/> <br/> <strong>Pyrefly</strong>: <a href="https://pyrefly.org?featured_on=talkpython" target="_blank" >pyrefly.org</a><br/> <strong>Pyrefly Documentation</strong>: <a href="https://pyrefly.org/en/docs/?featured_on=talkpython" target="_blank" >pyrefly.org</a><br/> <strong>Pyrefly Installation Guide</strong>: <a href="https://pyrefly.org/en/docs/installation/?featured_on=talkpython" target="_blank" >pyrefly.org</a><br/> <strong>Pyrefly IDE Guide</strong>: <a href="https://pyrefly.org/en/docs/IDE/?featured_on=talkpython" target="_blank" >pyrefly.org</a><br/> <strong>Pyrefly GitHub Repository</strong>: <a href="https://github.com/facebook/pyrefly?featured_on=talkpython" target="_blank" >github.com</a><br/> <strong>Pyrefly VS Code Extension</strong>: <a href="https://marketplace.visualstudio.com/items?itemName=meta.pyrefly&featured_on=talkpython" target="_blank" >marketplace.visualstudio.com</a><br/> <strong>Introducing Pyrefly: A New Type Checker and IDE Experience for Python</strong>: <a href="https://engineering.fb.com/2025/05/15/developer-tools/introducing-pyrefly-a-new-type-checker-and-ide-experience-for-python/?featured_on=talkpython" target="_blank" >engineering.fb.com</a><br/> <strong>Pyrefly on PyPI</strong>: <a href="https://pypi.org/project/pyrefly/?featured_on=talkpython" target="_blank" >pypi.org</a><br/> <strong>InfoQ Coverage: Meta Pyrefly Python Typechecker</strong>: <a href="https://infoq.com/news/2025/05/meta-pyrefly-python-typechecker/?featured_on=talkpython" target="_blank" >infoq.com</a><br/> <strong>Pyrefly Discord Invite</strong>: <a href="https://discord.gg/Cf7mFQtW7W?featured_on=talkpython" target="_blank" >discord.gg</a><br/> <strong>Python Typing Conformance (GitHub)</strong>: <a href="https://github.com/python/typing/tree/main/conformance?featured_on=talkpython" target="_blank" >github.com</a><br/> <strong>Typing Conformance Leaderboard (HTML Preview)</strong>: <a href="https://htmlpreview.github.io/?https://github.com/python/typing/blob/main/conformance/results/results.html&featured_on=talkpython" target="_blank" >htmlpreview.github.io</a><br/> <br/> <strong>Watch this episode on YouTube</strong>: <a href="https://www.youtube.com/watch?v=P4RKxl_giH4" target="_blank" >youtube.com</a><br/> <strong>Episode #523 deep-dive</strong>: <a href="https://talkpython.fm/episodes/show/523/pyrefly-fast-ide-friendly-typing-for-python#takeaways-anchor" target="_blank" >talkpython.fm/523</a><br/> <strong>Episode transcripts</strong>: <a href="https://talkpython.fm/episodes/transcript/523/pyrefly-fast-ide-friendly-typing-for-python" target="_blank" >talkpython.fm</a><br/> <br/> <strong>Theme Song: Developer Rap</strong><br/> <strong>🥁 Served in a Flask 🎸</strong>: <a href="https://talkpython.fm/flasksong" target="_blank" >talkpython.fm/flasksong</a><br/> <br/> <strong>---== Don't be a stranger ==---</strong><br/> <strong>YouTube</strong>: <a href="https://talkpython.fm/youtube" target="_blank" ><i class="fa-brands fa-youtube"></i> youtube.com/@talkpython</a><br/> <br/> <strong>Bluesky</strong>: <a href="https://bsky.app/profile/talkpython.fm" target="_blank" >@talkpython.fm</a><br/> <strong>Mastodon</strong>: <a href="https://fosstodon.org/web/@talkpython" target="_blank" ><i class="fa-brands fa-mastodon"></i> @talkpython@fosstodon.org</a><br/> <strong>X.com</strong>: <a href="https://x.com/talkpython" target="_blank" ><i class="fa-brands fa-twitter"></i> @talkpython</a><br/> <br/> <strong>Michael on Bluesky</strong>: <a href="https://bsky.app/profile/mkennedy.codes?featured_on=talkpython" target="_blank" >@mkennedy.codes</a><br/> <strong>Michael on Mastodon</strong>: <a href="https://fosstodon.org/web/@mkennedy" target="_blank" ><i class="fa-brands fa-mastodon"></i> @mkennedy@fosstodon.org</a><br/> <strong>Michael on X.com</strong>: <a href="https://x.com/mkennedy?featured_on=talkpython" target="_blank" ><i class="fa-brands fa-twitter"></i> @mkennedy</a><br/></div>

https://talkpython.fm/episodes/show/523/pyrefly-fast-ide-friendly-typing-for-python