yfinance is a mature Python library that provides programmatic access to Yahoo Finance market data. It is primarily an application/library, not a data research project, though it includes data repair and cleaning utilities. The library exposes a high-level API (Ticker, download, Search, Lookup, Market, Screener) that fetches historical prices, fundamentals, financial statements, holders, analysis, and more from Yahoo's various JSON endpoints. It handles Yahoo's quirks (cookie/crumb authentication, timezone issues, data errors) and includes a sophisticated price repair pipeline that detects and corrects common data anomalies like 100x unit mixups, bad stock splits, zero values, and dividend double-counting. The architecture is monolithic with modular scrapers and utilities. It has extensive test coverage (though currently failing in CI), active maintenance, and a large user base (25k+ stars). The codebase is well-structured with reusable utility functions, but some legacy artifacts (Travis CI, disabled pytest workflow) and heavy reliance on heuristic repair logic introduce medium technical drift.