FIX: Prevent crash when removing a subfigure containing subplots (matplotlib#31323)

* FIX: Prevent crash when removing a subfigure containing subplots

* Use attribute-based guard in Artist.remove

Author: Vikash-Kumar-23

lib/matplotlib/artist.py

@@ -255,10 +255,12 @@ def remove(self):
             # clear stale callback
             self.stale_callback = None
             _ax_flag = False
-            if hasattr(self, 'axes') and self.axes:
+            ax = getattr(self, 'axes', None)
+            mouseover_set = getattr(ax, '_mouseover_set', None)
+            if mouseover_set is not None:
                 # remove from the mouse hit list
-                self.axes._mouseover_set.discard(self)
-                self.axes.stale = True
+                mouseover_set.discard(self)
+                ax.stale = True
                 self.axes = None  # decouple the artist from the Axes
                 _ax_flag = True
 

lib/matplotlib/tests/test_figure.py

@@ -1576,6 +1576,7 @@ def test_subfigures_wspace_hspace():
 def test_subfigure_remove():
     fig = plt.figure()
     sfs = fig.subfigures(2, 2)
+    sfs[1, 1].subplots()
     sfs[1, 1].remove()
     assert len(fig.subfigs) == 3