rcParams

rcParams is a central configuration mechanism used by the Matplotlib plotting library. It is a mutable, dictionary-like object that stores runtime configuration parameters (RCP) which determine the default appearance and behavior of figures, axes, text, and other plot elements. The object is accessible through the Matplotlib API as matplotlib.rcParams or, in many cases, via matplotlib.pyplot.rcParams. Changes to rcParams affect subsequent plots in the running session unless overridden locally.

Users can read values from rcParams and modify them to customize style. Updates can be applied by direct assignment or by using a dictionary update, for example rcParams['figure.figsize'] = [8.0, 6.0] or rcParams.update({'font.size': 12}). These changes can be made globally for all plots or temporarily within a script. There is also rcParamsDefault, which holds the original default values before any user customization.

rcParams is organized into groups that reflect different aspects of a plot, such as figure, axes, lines, font, image, legend, and grid. Each group contains specific keys, like figure.figsize, axes.labelsize, font.family, and savefig.dpi, which provide sensible defaults that can be overridden as needed. Styles and themes in Matplotlib are ultimately implemented through rcParams, enabling consistent visual appearances across multiple figures or projects.

Configuration is also supported through matplotlibrc files, which can specify default rcParams at a global, user, or project level. These settings can be supplemented by style sheets and programmatic updates. Using rcParams provides a centralized, reproducible way to control the look and feel of plots without modifying individual plotting calls.