Don't leave empty dict containers behind when nested properties are set to None - #5637
Don't leave empty dict containers behind when nested properties are set to None#5637ahmojo wants to merge 2 commits into
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…et to None
Setting a nested property such as marker.colorbar.thicknessmode to None
left a residual empty {} container in the figure's props, which was then
emitted in the figure JSON. For splom traces this residual
marker.colorbar {} made a later Plotly.restyle of colorbar attributes
misconvert the colorbar thickness and collapse the scatter-matrix layout.
_set_in now treats removal of a non-existent path as a no-op and prunes
emptied dict parents, and property assignment to None prunes emptied
compound-child dicts (lists are preserved as positional placeholders).
Fixes plotly#5615
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Thanks for the PR! We'll take a look and follow up. We're a bit backed up at the moment, so it might take a while to get through it. |
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Hi @ahmojo, thanks for the contribution! This is an interesting change. Pruning empty dicts left behind after a value is removed by setting it to None in plotly_restyle() does seem to make sense at first glance, although I'm not sure what the practical effects are beyond possibly this particular bug. The reproduction example in #5637 never actually calls plotly_restyle() at all, since it uses the JavaScript Plotly.restyle() function, so I don't quite see how this change would affect the result of that particular example. Were you able to reproduce the issue in pure Python using plotly_restyle()? |
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Thanks for pointing this out @emilykl. I tested this with a live FigureWidget using only Python. A direct restyle on a pristine widget works normally, but the same set-and-clear history from the issue reproduces the collapse: widget = go.FigureWidget(make_fig()) display(widget) Then, after it renders: widget.data[1].marker.colorbar.thicknessmode = "pixels"
widget.data[1].marker.colorbar.thicknessmode = None
widget.plotly_restyle(
{"marker.colorbar.thicknessmode": "pixels"},
trace_indexes=[1],
)
The clear leaves colorbar: {} in the browser-side trace. The final restyle changes the thickness to 16,290px and shrinks the plot width from 543px to 64px. |
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Thanks @ahmojo for the follow-up! If this fixes an issue that only comes up when injecting JavaScript into a plotly.py chart, I'd prefer to hold off on this change for now. I'm open to merging it in the future if we can show that it fixes other more significant issues. |
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Link to issue
Related to #5615
Description of change
Setting a nested property to None after it had been set could leave an empty compound container in the emitted figure JSON. For example, clearing marker.colorbar.thicknessmode left marker: {"colorbar": {}}. The same residue could be created when plotly_restyle(..., None) targeted a never-set nested path, even though no restyle message was sent.
This is inconsistent with construction, where empty compound containers are already pruned. This PR makes removal of a missing path a no-op and prunes emptied scalar compound containers while preserving list positions.
In the static-HTML reproduction from #5615, removing that residue prevents it from being included in the initial payload and avoids the subsequent JavaScript restyle collapse. This does not change plotly.js itself: a live FigureWidget whose browser-side state already contains colorbar: {} can still collapse after a later restyle.
Demo
I isolated the Python serialization trigger using the issue's Playwright reproduction (1200x800 viewport, the same bundled plotly.js for every variant):
With this change, the static-HTML output matches the pristine control. The separate live-FigureWidget path remains a plotly.js/frontend-state issue and is outside the scope of this cleanup.
Testing strategy
Added two regression tests in tests/test_core/test_figure_messages/test_plotly_restyle.py:
Targeted checks:
Additional information (optional)
This changes serialized output for set-then-unset scalar compound properties across the library, bringing assignment and restyle cleanup in line with construction-time behavior. Compound-array/list entries remain in place as positional placeholders, and batch updates are pruned when the batch flushes.
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