Jelle Zijlstra
Member Of Technical Staff at OpenAI
Orinda, California, United States
Summary
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Top School
Top expert inPython Ecosystem Development and Data Science
Jelle Zijlstra is a pragmatic software engineer with 13 years of experience building developer-facing infrastructure and tooling, currently a Member of Technical Staff at OpenAI after a long tenure as Staff Engineer at Quora. He has deep expertise in Python internals and static typing—core developer on CPython, mypy, typeshed, typing-extensions, and a member of the Python Typing Council—plus notable contributions to Black and the high-performance linter Ruff. At Quora he led major migrations (Python 2→3), built the continuous deployment system, and authored an internal type checker, demonstrating a blend of systems thinking and developer productivity focus. His open-source work spans compiler-level changes (Cython f-string parsing), documentation and PEP edits, and rigorous type-stub maintenance, reflecting both low-level implementation skill and attention to usability. Based in Orinda, California, he pairs production-scale engineering with a knack for clarifying complex interfaces and edge-case behavior in widely used Python tooling.
13 years of coding experience
12 years of employment as a software developer
Stedelijk Gymnasium LeidenBachelor's, Biology, Bachelor's, Biology at Harvard University
English, German, Dutch, French, Spanish, Latin, Greek
Stackoverflow
340reputation
17kreached
8answers
3questions
Github Skills (53)
static-code-analysis10
static-typing10
typesc10
static-analysis10
type-inference10
type-check10
python10
ruff10
mypy10
technical-writing10
dynamic-typing10
typescript10
f-string10
implicit-typing10
refactor10
Programming languages (20)
Github contributions (5)
psf/black
May 2018 - Jan 2023
The uncompromising Python code formatter
Role in this project:
Back-end Developer
Back-end DeveloperContributions:24 releases, 1102 reviews, 152 commits in 4 years 9 months
Contributions summary:Jelle's commits primarily focused on refactoring and enhancing the codebase of the `black` Python code formatter. Their work included removing unnecessary prefixes and supporting Python Interface (`.pyi`) files and numeric literals. The user also addressed several bugs, like the handling of docstring whitespace and parenthesis. Moreover, they made improvements to existing code features, and increased the overall code quality.
pythonformattercodeformattergofmtyapf
python/typing
Jan 2017 - May 2022
Python static typing home. Hosts the documentation and a user help forum.
Role in this project:Back-end Developer
Back-end DeveloperContributions:415 reviews, 46 commits, 276 PRs in 5 years 4 months
Contributions summary:Jelle primarily contributed to the `python/typing` repository, enhancing Python's static typing capabilities. Their work included implementing new features like `NamedTuple` defaults and `AsyncGenerator` support. They also added `typing.Counter` and `typing.ChainMap` and addressed issues related to test execution and compatibility. The user consistently updated and adapted the typing library to improve its usability.
pythonstatic-typinggradual-typing
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