Previously when using thewebagg backend if you wanted to change the title above a figure you would usefigure.set_label('whatever') and if you usedfigure.canvas.manager.set_window_title('whatever') it would be ignored. This was inconsistent with other backends which use the latter.

This PR changes the behaviour so thatfigure.canvas.manager.set_window_title('whatever') is used now forwebagg, the same as the other backends.

There is no test as there isn't currently any visual testing of thewebagg backend. There is some draft work underway in#23540 for this. So here is a demonstration instead, using this code:

importmatplotlibasmplmpl.use('webagg')importmatplotlib.pyplotaspltfig1,ax1=plt.subplots(figsize=(3,2))ax1.plot([1,3,2,4])fig1.canvas.manager.set_window_title('My line plot')fig2,ax2=plt.subplots(figsize=(3,2))ax2.contourf([[1,2], [3,4]])fig2.canvas.manager.set_window_title('My contour plot')fig3,ax3=plt.subplots(figsize=(3,2))ax3.bar(x=[0,1],height=[1,2])plt.show()

thewebagg output is:

which is consistent with the output produced by e.g. theqtagg backend:

PR checklist

"closes[Bug]: canvas.manager.set_window_title does not work to figure withWebAgg backend #29256" is in the body of the PR description tolink the related issue
new and changed code istested
Plotting related features are demonstrated in anexample
New Features andAPI Changes are noted with adirective and release note
Documentation complies withgeneral anddocstring guidelines

Use set_window_title rather than set_label to set title of webagg figure

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github-actionsbot added the GUI: webagg label

Dec 17, 2024

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timhoffm commentedDec 17, 2024

What's the behavior with respect to the label? I assume the label is used as a fallback if the window title is not set?

If that's correct, the behavoir should be documented, with the comment that it results in backward compatibility for previous users ofset_label, butset_window_title is preferred overset_label.

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ianthomas23 commentedJan 2, 2025

What's the behavior with respect to the label? I assume the label is used as a fallback if the window title is not set?

Unfortunately it is not that simple. If the windowtitle is not set then the default such as"Figure 1" is used instead from here:

matplotlib/lib/matplotlib/backend_bases.py

Line 2612 inf2717a5

self.set_window_title(f"Figure{num:d}")

regardless of the backend used.

This can be overridden by passing alabel to theFigure constructor, but any subsequent use ofFigure.set_label does not update thetitle. This behaviour is surprising but it is, for good or bad, the same as for other backends such asqtagg.

To demonstrate this use

importmatplotlibasmplmpl.use("qtagg")#mpl.use('webagg')importmatplotlib.pyplotasplt# 1. Set title using set_window_titlefig1,ax1=plt.subplots(figsize=(3,2))fig1.canvas.manager.set_window_title('Using set_window_title')# 2. Set title using label passed to Figure constructorfig2,ax2=plt.subplots(figsize=(3,2),label="Label in constructor")# 3. Using Figure.set_label has no effect on the window titlefig3,ax3=plt.subplots(figsize=(3,2))fig3.set_label("This is not used in the title")plt.show()

and the title outputs are the same forqtagg andwebagg here:

So this PR bringswebagg in line with other backends. WhetherFigure.set_label should also update the title (for all backends) would I think be a separate issue for discussion.