matplotlib.tight_layout.auto_adjust_subplotpars can return None now if the new subplotparams will collapse axes to zero width or height. This prevents tight_layout from being executed. Similarly matplotlib.tight_layout.get_tight_layout_figure will return None.

To improve import (startup) time, private modules are now imported lazily. These modules are no longer available at these locations:

• matplotlib.backends.backend_agg._png
• matplotlib.contour._contour
• matplotlib.image._png
• matplotlib.mathtext._png
• matplotlib.testing.compare._png
• matplotlib.texmanager._png
• matplotlib.tri.triangulation._tri
• matplotlib.tri.triangulation._qhull
• matplotlib.tri.tricontour._tri
• matplotlib.tri.trifinder._tri