eslothower · eslothower · May 2, 2023 · Apr 25, 2023 · Apr 25, 2023 · Apr 25, 2023
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -649,6 +649,8 @@ def set_hover(self, hover):
               artist will fire a hover event if the mouse event is hovering over
               the artist.
         """
+        if not self.figure and hover is not None:
+            raise ValueError("Cannot hover without an existing figure")
         self._hover = hover
 
     def get_hover(self):

diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -3016,8 +3016,9 @@ def mouse_move(self, event):
         self.set_message(self._mouse_event_to_message(event))
 
         if callable(getattr(self, 'set_hover_message', None)):
-            for a in self.canvas.figure.findobj(match=lambda x: not isinstance(x,
-                                                Rectangle), include_self=False):
+            def nonrect(x):
+                return not isinstance(x, Rectangle)
+            for a in self.canvas.figure.findobj(match=nonrect, include_self=False):
                 inside, prop = a.contains(event)
                 if inside:
                     self.set_hover_message(self._mouse_event_to_message(event))

diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
@@ -9,7 +9,7 @@
 from matplotlib.backend_bases import (
     _Backend, FigureCanvasBase, FigureManagerBase, NavigationToolbar2,
     TimerBase, cursors, ToolContainerBase, MouseButton,
-    CloseEvent, KeyEvent, LocationEvent, MouseEvent, ResizeEvent)
+    CloseEvent, KeyEvent, LocationEvent, MouseEvent, ResizeEvent, HoverEvent)
 import matplotlib.backends.qt_editor.figureoptions as figureoptions
 from . import qt_compat
 from .qt_compat import (
@@ -305,6 +305,17 @@ def mouseReleaseEvent(self, event):
                        modifiers=self._mpl_modifiers(),
                        guiEvent=event)._process()
 
+    def mouseOverEvent(self, event):
+        artist = event.artist
+        if not artist.get_hover:
+            thismouse = MouseEvent("motion_hover_event", self,
+                                   *self.mouseEventCoords(event),
+                                   modifiers=self._mpl_modifiers(),
+                                   guiEvent=event)
+            hovering = HoverEvent("motion_hover_event", self,
+                                  thismouse, artist, None)
+            hovering._process()
+
     def wheelEvent(self, event):
         # from QWheelEvent::pixelDelta doc: pixelDelta is sometimes not
         # provided (`isNull()`) and is unreliable on X11 ("xcb").

diff --git a/lib/matplotlib/tests/test_artist.py b/lib/matplotlib/tests/test_artist.py
@@ -325,6 +325,24 @@ def test_set_alpha_for_array():
         art._set_alpha_for_array([0.5, np.nan])
 
 
+def test_set_hover():
+    art = martist.Artist()  # blank canvas
+    with pytest.raises(ValueError, match="Cannot hover without an existing figure"):
+        art.set_hover(True)
+
+    fig, ax = plt.subplots()
+    im = ax.imshow(np.arange(36).reshape(6, 6))  # non-blank canvas
+
+    im.set_hover(True)  # set hover variable to possible values given a figure exists
+    assert im.get_hover()
+    im.set_hover(False)
+    assert not im.get_hover()
+    im.set_hover(None)
+    assert im.get_hover() is None
+
+    im.remove()
+
+
 def test_callbacks():
     def func(artist):
         func.counter += 1