structlog is a production-caliber structured logging library for Python. It decouples log event construction from output formatting using a composable processor chain — each processor receives a mutable event dictionary (with keys like event, log_level, timestamp, and custom fields) and can filter, enrich, or render it. The library provides a proxy-based bound logger (structlog.get_logger()) that lazily assembles the final logger with frozen context, supporting immutable bind/unbind operations suitable for safe usage across async and threaded code. Two context management backends exist: structlog.contextvars (recommended) for modern async-safe context propagation, and structlog.threadlocal (deprecated) for legacy thread-local patterns. The architecture centers on three global configuration axes: processors (a list of callables), wrapper class (the bound logger implementation), and logger factory (which creates the underlying output target). Built-in processors include JSONRenderer, ConsoleRenderer (with colorful column-based output), KeyValueRenderer, TimeStamper, CallsiteParameterAdder, and ExceptionRenderer. Specialized integration modules connect to Python's standard library logging (structlog.stdlib) and Twisted (structlog.twisted), allowing structlog to serve as a drop‑in replacement for existing logging configurations while adding structured capabilities like structured tracebacks and filterable log levels. Testing support is built in via structlog.testing, which provides a capture_logs() context manager and a CapturingLogger for asserting log output in unit tests without side effects.