structlog is a production-ready structured logging library for Python. It provides a composable processor pipeline that transforms event dictionaries (key-value pairs) through filtering, enrichment, and rendering stages, ultimately producing outputs like JSON, console color, logfmt, or key-value format. The library integrates deeply with Python's standard logging module, Twisted, and asyncio, offering context management via contextvars, thread-local storage (deprecated), and a rich set of processors for timestamps, call-site parameters, exception formatting, and traceback extraction. Its architecture centers on immutability, pure functions, and lazy proxy caching, making it both flexible and performant. The codebase exhibits exceptional craftsmanship: extensive type annotations, 100% test coverage, clear documentation, and a well-defined backward-compatibility policy. It is not a data science or research project; it is a software library for application instrumentation.