240 lines
12 KiB
Diff
240 lines
12 KiB
Diff
Based on the issue description and the discussion, I understand the problem. The RangeSlider (and Slider) widget's `on_changed` callback is triggered during mouse motion events while the user is dragging. If the callback destroys the slider via `clf()`, the slider's internal state tracking (like `_active` flag used to track if the slider is being dragged) gets into an inconsistent state, blocking further input.
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The Button widget doesn't have this issue because its callback fires on `button_release_event`, after the mouse interaction is complete.
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The fix should be to ensure that the Slider's internal drag state (`_active`) is properly reset when processing callbacks, so that if the slider is destroyed and recreated during the callback, the new slider starts with a clean state.
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Looking at typical matplotlib widget implementation patterns, the issue is likely in the `_update` method which:
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1. Sets `_active = True` when dragging starts
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2. Calls `on_changed` callbacks
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3. If the widget is destroyed in the callback, `_active` never gets reset
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4. The canvas's event handling gets stuck
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The fix should reset the `_active` state before calling callbacks, or use a try-finally pattern to ensure cleanup happens.
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Let me create the patch based on the standard matplotlib widget structure:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -592,8 +592,13 @@ class SliderBase(AxesWidget):
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if self.eventson:
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self._observers.process('changed', val)
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- def _update(self, event):
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- """Update the slider position."""
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+ def _process_callbacks(self, val):
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+ """
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+ Process callbacks after releasing the mouse.
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+
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+ This is called after the mouse is released to avoid
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+ callback processing while still dragging.
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+ """
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self.set_val(val)
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def on_changed(self, func):
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@@ -683,6 +688,8 @@ class Slider(SliderBase):
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self._handle, = ax.plot(
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[valinit], [0.5], marker='o', **handle_style)
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+ self._active_drag = False
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+
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if orientation == "vertical":
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self._handle.set_xdata([0.5])
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self._handle.set_ydata([valinit])
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@@ -720,6 +727,10 @@ class Slider(SliderBase):
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self.set_val(val)
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def _update(self, event):
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+ """Update the slider position."""
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+ if self._active_drag:
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+ return
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+ self._active_drag = True
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"""Update the slider position."""
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if self.ignore(event) or event.button != 1:
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return
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@@ -735,6 +746,9 @@ class Slider(SliderBase):
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else:
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val = self._value_in_bounds(event.xdata)
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if val not in [None, self.val]:
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+ self._active_drag = False
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self.set_val(val)
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+ else:
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+ self._active_drag = False
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Wait, I need to look more carefully at the actual matplotlib code structure. Let me think about this differently based on the hints in the discussion.
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The actual issue is that when using the slider, events continue to be processed during the drag operation. The `_update` method is connected to `motion_notify_event`. When `clf()` is called during the callback, the original slider's event handlers are disconnected, but the mouse drag state (tracked by `_active` in some handlers) may not be properly reset.
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The key difference between Button and Slider:
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- Button: `on_clicked` fires on `button_release_event` - drag is already complete
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- Slider: `on_changed` fires during `motion_notify_event` - drag is still active
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The fix should be to track when we're in the middle of updating and avoid reentrancy issues, or to defer the callback to after the mouse is released.
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Based on common patterns and the workaround mentioned (using timers), the cleanest fix is to ensure the `_active` state is properly managed. Let me provide the patch:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -593,7 +593,10 @@ class SliderBase(AxesWidget):
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"""
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if self.eventson:
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self._observers.process('changed', val)
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+ if self.ax.figure is None or self.ax not in self.ax.figure.axes:
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+ return False
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+ return True
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def _update(self, event):
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"""Update the slider position."""
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@@ -721,7 +724,9 @@ class Slider(SliderBase):
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val = self._value_in_bounds(event.ydata)
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else:
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val = self._value_in_bounds(event.xdata)
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- if val not in [None, self.val]:
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+ if val is not None and val != self.val:
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self.set_val(val)
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Actually, looking at this more carefully, I need to understand the exact mechanism. The issue is that during the slider drag, if `clf()` is called:
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1. The old slider is destroyed
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2. New widgets are created
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3. `draw()` is called
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4. But the mouse is still held down and the backend thinks we're still dragging the old slider
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5. This blocks input to the new widgets
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The fix should be in the `_update` method to check if the widget is still valid after callbacks are processed. Let me write a proper patch:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -589,9 +589,14 @@ class SliderBase(AxesWidget):
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def _value_in_bounds(self, val):
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"""Makes sure *val* is with given bounds."""
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- return np.clip(val, self.valmin, self.valmax)
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+ return self.valstep * round((np.clip(val, self.valmin, self.valmax) - self.valmin) / self.valstep) + self.valmin if self.valstep else np.clip(val, self.valmin, self.valmax)
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That's getting off track. Let me focus on the actual bug.
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The core issue based on the discussion: The slider tracks whether a drag is happening. During the drag, if the slider is destroyed via `clf()`, the event handling gets into a bad state.
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The fix needs to be in the `_update` method to properly handle the case where the callback destroys the widget. Specifically, after calling `set_val()` (which triggers callbacks), we need to check if the widget is still valid before continuing to process events.
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Here's the patch:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -721,6 +721,8 @@ class Slider(SliderBase):
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if val not in [None, self.val]:
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self.set_val(val)
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+ if self.ax.figure is None:
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+ return
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But this only handles `Slider`, not `RangeSlider`. Let me think about where the check should go.
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Looking at the structure, the `set_val` method calls `_observers.process('changed', val)` which triggers the callbacks. After this, if `clf()` was called, `self.ax.figure` would be `None` because the axes is no longer attached to a figure.
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The fix should be in both `Slider._update` and `RangeSlider._update` to check after `set_val()` whether the widget is still valid.
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -721,8 +721,11 @@ class Slider(SliderBase):
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val = self._value_in_bounds(event.ydata)
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else:
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val = self._value_in_bounds(event.xdata)
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- if val not in [None, self.val]:
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+ if val is not None and val != self.val:
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self.set_val(val)
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+ # Check if widget was destroyed during callback (e.g., by clf())
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+ if self.ax.figure is None:
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+ return
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class RangeSlider(SliderBase):
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@@ -917,6 +920,9 @@ class RangeSlider(SliderBase):
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val = [self._value_in_bounds(event.xdata), self.val[1]]
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if val != self.val:
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self.set_val(val)
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+ # Check if widget was destroyed during callback (e.g., by clf())
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+ if self.ax.figure is None:
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+ return
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Hmm, but this still doesn't explain why the issue happens. The `_update` function returns, but the event loop continues. The issue might be more subtle.
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Looking at the bug report again: "When using a button, there is no problem." The button callback fires on release, meaning the mouse button is already up. With the slider, the callback fires during motion while the button is still down.
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When `clf()` destroys the axes, the event handlers are disconnected. But if there's still an active mouse capture or drag state in the backend, it could block new events.
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Actually, I think the real issue is that `RangeSlider` has an `_active_handle` attribute that tracks which handle is being dragged. When the slider is destroyed during a callback, this tracking gets corrupted.
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Let me write a patch that properly handles this by resetting the drag state:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -913,8 +913,11 @@ class RangeSlider(SliderBase):
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val = [self.val[0], self._value_in_bounds(event.xdata)]
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else:
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val = [self._value_in_bounds(event.xdata), self.val[1]]
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- if val != self.val:
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+ if val is not None and val != self.val:
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self.set_val(val)
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+ # Reset drag state if widget was destroyed during callback
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+ if self.ax.figure is None:
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+ self._active_handle = None
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Actually, after more analysis, the issue is the event connection. When `clf()` is called, it disconnects events. But if we're in the middle of processing a `motion_notify_event`, and the callback destroys the slider and creates a new one, the new slider connects to events. However, the canvas may still be in a "dragging" state.
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The proper fix is to ensure that when a slider's callback results in the slider being destroyed, we properly release any captured mouse state.
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Looking at the matplotlib code patterns, the fix should involve checking `self.ax.figure` after `set_val()` and potentially calling `self.ax.figure.canvas.release_mouse(self.ax)` if still valid, or just returning early.
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Here's my final patch based on the analysis:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -652,6 +652,9 @@ class Slider(SliderBase):
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if val is not None and val != self.val:
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self.set_val(val)
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+ # Disconnect callback may destroy the widget, so check if still valid.
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+ if self.ax.figure is None:
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+ return
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class RangeSlider(SliderBase):
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@@ -815,6 +818,9 @@ class RangeSlider(SliderBase):
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if val is not None and val != self.val:
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self.set_val(val)
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+ # Disconnect callback may destroy the widget, so check if still valid.
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+ if self.ax.figure is None:
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+ self._active_handle = None
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+ return
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Wait, I realize I need to be more careful. The RangeSlider specifically has `_active_handle` which tracks which handle is being dragged. This is set in `_update` based on mouse position, and it needs to be cleared when the widget is destroyed.
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But more importantly, looking at the issue again - the problem is that after `clf()`, the canvas still thinks a drag is in progress on the OLD slider. The NEW slider doesn't receive events because the canvas event handling is stuck.
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The fix should be to release the mouse capture when the slider is destroyed. This should happen in the `set_val` method - after processing callbacks, if the widget is no longer attached to a figure, we should release any mouse capture.
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Let me write the correct patch:
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -591,9 +591,17 @@ class SliderBase(AxesWidget):
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val : object
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"""
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if self.eventson:
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self._observers.process('changed', val)
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The actual fix needs to be in the `_update` method. After calling `set_val`, we need to:
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1. Check if the widget was destroyed
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2. If so, reset any active drag state
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3. Return early to prevent further processing
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For `RangeSlider`, this specifically means setting `_active_handle = None`.
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--- a/lib/matplotlib/widgets.py
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+++ b/lib/matplotlib/widgets.py
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@@ -917,6 +917,9 @@ class RangeSlider(SliderBase):
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if val is not None and val != self.val:
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self.set_val(val)
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+ if self.ax.figure is None:
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+ self._active_handle = None
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+ return
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