legend.linewidth rcParam and parameter

A new rcParam legend.linewidth has been added to control the line width of the legend's box edges. When set to None (the default), it inherits the value from patch.linewidth. This allows for independent control of the legend frame line width without affecting other elements.

The Legend constructor also accepts a new linewidth parameter to set the legend frame line width directly, overriding the rcParam value.

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([1, 2, 3], label='data')
ax.legend(linewidth=2.0)  # Thick legend box edge
plt.show()

(Source code, 2x.png, png)