fix(plot): default to environment-managed Matplotlib display - #84

Up to standards ✅

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Thank you for your interest in pgraph-python, and for this contribution. This brings plot() and highlight_path() in line with the block= contract used across the RVC toolboxes (None leaves display to the environment, False shows without waiting, True waits). RTB's planners already default to None, and PRMPlanner.plot in particular calls Graph.plot without a block, so it should now behave properly. The three-state tests are just what is needed.

I'm happy to take this as a deliberate behaviour change. Before merging, could you:

1. Mark the change in the docstrings. Add a .. versionchanged:: 1.1 note to both plot() and highlight_path() saying the default changed from False to None, so plt.show() is no longer called unless block is given, and how to get the old behaviour (block=False).
2. Add a CHANGELOG entry in a new Unreleased section at the top of the file (this will become 1.1.0), under a "Behaviour change" heading, naming who is affected: anyone who called g.plot() in a script or an IPython terminal (without %matplotlib or plt.ion()) and relied on a window appearing. They now need plt.show(), or block=False.
3. Update the other docs and examples that show plotting: examples/roads.ipynb (it can drop its explicit block=None) and any runblock or other examples in docs/ that call plot() or highlight_path(). Please check that they still produce a figure.
4. Link the issue and expand the description: please add Fixes #79 and say what the old behaviour was and what you changed.
5. Test the other mix: plot() with the default followed by highlight_path(block=False), and plot(block=None, ax=...) with a caller-supplied axes.

Thanks again, and let me know if you'd rather I made any of these changes myself.

Hi Peter,

I've pushed the requested updates. Both plotting methods now have versionchanged:: 1.1 notes, and the CHANGELOG explains the behaviour change for scripts and IPython users. I've also updated the documentation and examples, with regression tests covering both mixed-use cases you mentioned.

The branch is up to date with main, and fork CI passed: https://github.com/huxiaoyi-ovo/pgraph-python/actions/runs/41379496007

Could you approve the upstream CI run when convenient? Thanks for the detailed review!

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.12%. Comparing base (0c33e9b) to head (998bdfd).
⚠️ Report is 1 commits behind head on main.

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