plotnine is a mature Python library that implements the Grammar of Graphics, closely modeled after R's ggplot2. It provides a declarative, layered API for building statistical visualizations: users compose plots by adding geometric objects (geoms), statistical transformations (stats), scales, coordinate systems, facets, themes, and guides using the `+` operator. The library renders all output through matplotlib, supporting a wide range of plot types (scatter, bar, line, histogram, density, boxplot, violin, contour, maps, etc.) with extensive customization via themes and scales. It includes built-in example datasets, animation support, plot composition (arranging multiple plots), and integration with Jupyter/Quarto. The codebase is well-structured with a clear separation of concerns (geoms, stats, scales, coords, facets, themes, guides, composition) and employs several reusable design patterns such as a registry metaclass for automatic subclass registration, dataclass-based scale definitions, a hierarchical themeable system, and a docstring generation decorator. External dependencies include matplotlib, pandas, numpy, scipy, statsmodels, mizani, and contourpy, with optional support for adjustText, geopandas, and skmisc. The project is actively maintained with weekly CI tests against bleeding-edge dependencies and a comprehensive test suite using baseline image comparison.