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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
Mypy and pyright both use it. mypy's codebase is reasonably readable and not that big. https://github.com/python/mypy/wiki/Implementation-Overview summarizes mypy implementation and which are the key files to read over if you want to see core type checker logic.
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