See in #22547

MatplotlibDeprecationWarning: Axes3D(fig) adding itself to the figure is deprecated since 3.4. Pass the keyword argument auto_add_to_figure=False and use fig.add_axes(ax) to suppress this warning. The default value of auto_add_to_figure will change to False in mpl3.5 and True values will no longer work in 3.6.  This is consistent with other Axes classes

We need to replace a line like this:

ax = Axes3D(fig, elev=elev, azim=azim, rect=[0, 0, 0.95, 1])

by:

ax = fig.add_subplot(111, projection="3d", elev=elev, azim=azim)
ax.set_position([0, 0, 0.95, 1])

For matplotlib < 3.2 (matplotlib 3.1.2 is our minimum supported version of matplotlib) we need to have this import:

# unused but required import for doing 3d projections with matplotlib < 3.2
import mpl_toolkits.mplot3d  # noqa: F401

see #22594 (comment) for more details.

List of examples affected

through git grep Axes3D examples:

• examples/cluster/plot_cluster_iris.py DOC: get rid of matplotlib DeprecationWarning in plot_cluster_iris.py #22594
• examples/cluster/plot_ward_structured_vs_unstructured.py DOC fix matplotlib warning for plot_ward_structured_vs_unstructured.py  #22631
• examples/datasets/plot_iris_dataset.py DOC Fix matplotlib warning for plot_iris_dataset.py #22640
• examples/decomposition/plot_pca_3d.py DOC Fix matplotlib warning for plot_pca_3d.py #22591
• examples/decomposition/plot_pca_iris.py DOC Fix axes3d matplotlib deprecation warning #22622
• examples/inspection/plot_partial_dependence.py EXA: remove deprecation warning for plot_partial_dependence #22654
• examples/manifold/plot_compare_methods.py done as part of DOC use notebook-style and fix matplotlib warning for plot_compare_methods #22679
• examples/manifold/plot_manifold_sphere.py

If you are interested to work on this issue

• mention in a comment which file you want to work on, so that different people can work on this issue in parallel
• open a PR changing only this file