Use set_window_title rather than set_label to set title of webagg figure #29338

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Merged

timhoffm merged 1 commit into matplotlib:main from ianthomas23:29256-webagg-set-window-title

Jan 7, 2025

Merged

Use set_window_title rather than set_label to set title of webagg figure #29338

timhoffm merged 1 commit into matplotlib:main from ianthomas23:29256-webagg-set-window-title

Jan 7, 2025

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ianthomas23

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@ianthomas23 ianthomas23 commented Dec 17, 2024

Closes #29256.

Previously when using the webagg backend if you wanted to change the title above a figure you would use figure.set_label('whatever') and if you used figure.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 that figure.canvas.manager.set_window_title('whatever') is used now for webagg, the same as the other backends.

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

import matplotlib as mpl
mpl.use('webagg')
import matplotlib.pyplot as plt
fig1, 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()

the webagg output is:

Screenshot 2024年12月17日 at 17 01 44

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

Screenshot 2024年12月17日 at 17 02 26

PR checklist

"closes [Bug]: canvas.manager.set_window_title does not work to figure with WebAgg backend #29256 " 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

@ianthomas23


 Use set_window_title rather than set_label to set title of webagg figure

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@github-actions github-actions bot added the GUI: webagg label

Dec 17, 2024

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timhoffm commented Dec 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 of set_label, but set_window_title is preferred over set_label.

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ianthomas23 commented Jan 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 window title is not set then the default such as "Figure 1" is used instead from here:

matplotlib/lib/matplotlib/backend_bases.py

Line 2612 in f2717a5

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

regardless of the backend used.

This can be overridden by passing a label to the Figure constructor, but any subsequent use of Figure.set_label does not update the title. This behaviour is surprising but it is, for good or bad, the same as for other backends such as qtagg.

To demonstrate this use

import matplotlib as mpl
mpl.use("qtagg")
#mpl.use('webagg')
import matplotlib.pyplot as plt
# 1. Set title using set_window_title
fig1, ax1 = plt.subplots(figsize=(3, 2))
fig1.canvas.manager.set_window_title('Using set_window_title')
# 2. Set title using label passed to Figure constructor
fig2, ax2 = plt.subplots(figsize=(3, 2), label="Label in constructor")
# 3. Using Figure.set_label has no effect on the window title
fig3, 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 for qtagg and webagg here:
Screenshot 2025年01月02日 at 14 47 19
Screenshot 2025年01月02日 at 14 46 26

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