Merge pull request matplotlib#31431 from buddy0452004/fix-contour-remove-crash-v2

FIX: Guard against already-removed labels in ContourSet.remove()

Author: ksunden

lib/matplotlib/contour.py

@@ -143,6 +143,11 @@ def clabel(self, levels=None, *,
         -------
         labels
             A list of `.Text` instances for the labels.
+
+            Note: The returned Text instances should not be individually
+            removed or have their geometry modified, e.g. by changing text or font size.
+            If you need such a modification, remove the entire
+            `.ContourSet` and recreate it.
         """
 
         if self.filled:
@@ -515,7 +520,14 @@ def labels(self, inline, inline_spacing):
     def remove(self):
         super().remove()
         for text in self.labelTexts:
-            text.remove()
+            try:
+                text.remove()
+            except ValueError:
+                _api.warn_external(
+                    "Some labels were manually removed from the ContourSet. "
+                    "To remove labels cleanly, remove the entire ContourSet "
+                    "and recreate it.")
+        self.labelTexts.clear()
 
 
 def _find_closest_point_on_path(xys, p):

lib/matplotlib/tests/test_contour.py

@@ -803,6 +803,15 @@ def test_contour_remove():
     assert ax.get_children() == orig_children
 
 
+def test_contour_remove_with_labels():
+    ax = plt.figure().add_subplot()
+    cs = ax.contour(np.arange(16).reshape((4, 4)))
+    labels = cs.clabel()
+    labels[0].remove()
+    with pytest.warns(UserWarning, match="Some labels were manually removed"):
+        cs.remove()
+
+
 def test_contour_no_args():
     fig, ax = plt.subplots()
     data = [[0, 1], [1, 0]]