How We Extended Polars with Rust Expression Plugins for fenic

Extending Polars with Rust Expression Plugins

Building fenic, a semantic DataFrame library for AI pipelines, required operations Polars lacked natively. Python UDFs were too slow and broke query composition. We solved this by writing nine Rust expression plugins using pyo3-polars. These plugins run in-engine over Arrow, preserve types, and compose seamlessly with native Polars operations, eliminating Python round-trips for text processing tasks like tokenization and JSON parsing.