Fix pickling of AxesWidgets.

There's no need to hold onto the (non-picklable) canvas as an attribute.

Author: anntzer

lib/matplotlib/tests/test_pickle.py

@@ -307,3 +307,11 @@ def test_cycler():
     ax = pickle.loads(pickle.dumps(ax))
     l, = ax.plot([3, 4])
     assert l.get_color() == "m"
+
+
+# Run under an interactive backend to test that we don't try to pickle the
+# (interactive and non-picklable) canvas.
+@pytest.mark.backend('tkagg')
+def test_axeswidget_interactive():
+    ax = plt.figure().add_subplot()
+    pickle.dumps(mpl.widgets.Button(ax, "button"))

lib/matplotlib/widgets.py

@@ -90,22 +90,6 @@ def ignore(self, event):
         """
         return not self.active
 
-    def _changed_canvas(self):
-        """
-        Someone has switched the canvas on us!
-
-        This happens if `savefig` needs to save to a format the previous
-        backend did not support (e.g. saving a figure using an Agg based
-        backend saved to a vector format).
-
-        Returns
-        -------
-        bool
-           True if the canvas has been changed.
-
-        """
-        return self.canvas is not self.ax.figure.canvas
-
 
 class AxesWidget(Widget):
     """
@@ -131,9 +115,10 @@ class AxesWidget(Widget):
 
     def __init__(self, ax):
         self.ax = ax
-        self.canvas = ax.figure.canvas
         self._cids = []
 
+    canvas = property(lambda self: self.ax.figure.canvas)
+
     def connect_event(self, event, callback):
         """
         Connect a callback function with an event.
@@ -1100,7 +1085,7 @@ def __init__(self, ax, labels, actives=None, *, useblit=True,
 
     def _clear(self, event):
         """Internal event handler to clear the buttons."""
-        if self.ignore(event) or self._changed_canvas():
+        if self.ignore(event) or self.canvas.is_saving():
             return
         self._background = self.canvas.copy_from_bbox(self.ax.bbox)
         self.ax.draw_artist(self._checks)
@@ -1677,7 +1662,7 @@ def __init__(self, ax, labels, active=0, activecolor=None, *,
 
     def _clear(self, event):
         """Internal event handler to clear the buttons."""
-        if self.ignore(event) or self._changed_canvas():
+        if self.ignore(event) or self.canvas.is_saving():
             return
         self._background = self.canvas.copy_from_bbox(self.ax.bbox)
         self.ax.draw_artist(self._buttons)
@@ -1933,7 +1918,7 @@ def __init__(self, ax, *, horizOn=True, vertOn=True, useblit=False,
 
     def clear(self, event):
         """Internal event handler to clear the cursor."""
-        if self.ignore(event) or self._changed_canvas():
+        if self.ignore(event) or self.canvas.is_saving():
             return
         if self.useblit:
             self.background = self.canvas.copy_from_bbox(self.ax.bbox)
@@ -2573,9 +2558,7 @@ def __init__(self, ax, onselect, direction, *, minspan=0, useblit=False,
         self.drag_from_anywhere = drag_from_anywhere
         self.ignore_event_outside = ignore_event_outside
 
-        # Reset canvas so that `new_axes` connects events.
-        self.canvas = None
-        self.new_axes(ax, _props=props)
+        self.new_axes(ax, _props=props, _init=True)
 
         # Setup handles
         self._handle_props = {
@@ -2588,14 +2571,12 @@ def __init__(self, ax, onselect, direction, *, minspan=0, useblit=False,
 
         self._active_handle = None
 
-    def new_axes(self, ax, *, _props=None):
+    def new_axes(self, ax, *, _props=None, _init=False):
         """Set SpanSelector to operate on a new Axes."""
         self.ax = ax
-        if self.canvas is not ax.figure.canvas:
+        if _init or self.canvas is not ax.figure.canvas:
             if self.canvas is not None:
                 self.disconnect_events()
-
-            self.canvas = ax.figure.canvas
             self.connect_default_events()
 
         # Reset

lib/matplotlib/widgets.pyi

@@ -33,8 +33,9 @@ class Widget:
 
 class AxesWidget(Widget):
     ax: Axes
-    canvas: FigureCanvasBase | None
     def __init__(self, ax: Axes) -> None: ...
+    @property
+    def canvas(self) -> FigureCanvasBase | None: ...
     def connect_event(self, event: Event, callback: Callable) -> None: ...
     def disconnect_events(self) -> None: ...
 
@@ -310,7 +311,6 @@ class SpanSelector(_SelectorWidget):
     grab_range: float
     drag_from_anywhere: bool
     ignore_event_outside: bool
-    canvas: FigureCanvasBase | None
     def __init__(
         self,
         ax: Axes,
@@ -330,7 +330,13 @@ class SpanSelector(_SelectorWidget):
         ignore_event_outside: bool = ...,
         snap_values: ArrayLike | None = ...,
     ) -> None: ...
-    def new_axes(self, ax: Axes, *, _props: dict[str, Any] | None = ...) -> None: ...
+    def new_axes(
+        self,
+        ax: Axes,
+        *,
+        _props: dict[str, Any] | None = ...,
+        _init: bool = ...,
+    ) -> None: ...
     def connect_default_events(self) -> None: ...
     @property
     def direction(self) -> Literal["horizontal", "vertical"]: ...