PR summary

This PR adds a new parameter framelinewidth to the legend() function to control the line width of the legend frame. This addresses issue #30095 where users requested the ability to customize the legend frame's line width.

Why is this change necessary?

Currently, users cannot customize the line width of the legend frame, which limits the visual customization options available for legends. This change provides more flexibility in legend styling.

What problem does it solve?

It solves the limitation where users cannot adjust the thickness of the legend frame border, allowing for better visual customization of legends to match different plot styles and preferences.

What is the reasoning for this implementation?

The implementation follows matplotlib's existing pattern of style customization parameters. It adds a new parameter framelinewidth that works similarly to other line width parameters in matplotlib, maintaining consistency with the library's API design.

Example:

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 100)
plt.plot(x, np.sin(x), label='sin(x)')
plt.plot(x, np.cos(x), label='cos(x)')

# Create legend with custom frame line width
plt.legend(framelinewidth=2.0)  # Thicker frame
plt.show()

PR checklist

• "closes [ENH]: Add parameter to set line width of legend frame #30095" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines