PR summary

This PR fixes a bug in PolygonSelector where box_handle_props is incorrectly set to None because dict.update() returns None. Discovered while working on #31623.

Why is this change necessary? / What problem does it solve?

When using PolygonSelector with draw_bounding_box=True, any provided box_handle_props are not applied correctly. Instead the bounding box handles fall back to default props from RectangleSelector.

What is the reasoning for this implementation?

The fix ensures box_handle_props inherits from handle_props, overrides are applied correctly, and the original handle_props dictionary is not mutated.

Example

The issue can be reproduced by specifying box_handle_props:

import matplotlib.pyplot as plt
from matplotlib.widgets import PolygonSelector

fig, ax = plt.subplots()

box_handle_props = dict(marker='o', markerfacecolor='g', markeredgecolor='b')

selector = PolygonSelector(ax, draw_bounding_box=True,
                           box_handle_props=box_handle_props)

selector.verts = [(0.3, 0.3), (0.7, 0.4), (0.4, 0.8)]

plt.show()

AI Disclosure

None.

PR checklist

• [N/A] "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• [N/A] Plotting related features are demonstrated in an example
• [N/A] New Features and API Changes are noted with a directive and release note
• [N/A] Documentation complies with general and docstring guidelines