From 9f6f71d79ad62d3b4ce7d6ed25c86992e54f253b Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 11 Aug 2020 20:36:33 -0400
Subject: [PATCH 1/4] Simplify some checks in widgets.

---
 lib/matplotlib/widgets.py | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
index 68bc543ba152..1ce7061dbed6 100644
--- a/lib/matplotlib/widgets.py
+++ b/lib/matplotlib/widgets.py
@@ -311,14 +311,13 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
         super().__init__(ax)
 
         if slidermin is not None and not hasattr(slidermin, 'val'):
-            raise ValueError("Argument slidermin ({}) has no 'val'"
-                             .format(type(slidermin)))
+            raise ValueError(
+                f"Argument slidermin ({type(slidermin)}) has no 'val'")
         if slidermax is not None and not hasattr(slidermax, 'val'):
-            raise ValueError("Argument slidermax ({}) has no 'val'"
-                             .format(type(slidermax)))
-        if orientation not in ['horizontal', 'vertical']:
-            raise ValueError("Argument orientation ({}) must be either"
-                             "'horizontal' or 'vertical'".format(orientation))
+            raise ValueError(
+                f"Argument slidermax ({type(slidermax)}) has no 'val'")
+        cbook._check_in_list(['horizontal', 'vertical'],
+                             orientation=orientation)
 
         self.orientation = orientation
         self.closedmin = closedmin
@@ -629,8 +628,8 @@ def set_active(self, index):
         ValueError
             If *index* is invalid.
         """
-        if not 0 <= index < len(self.labels):
-            raise ValueError("Invalid CheckButton index: %d" % index)
+        if index not in range(len(self.labels)):
+            raise ValueError(f'Invalid CheckButton index: {index}')
 
         l1, l2 = self.lines[index]
         l1.set_visible(not l1.get_visible())
@@ -1045,8 +1044,8 @@ def set_active(self, index):
 
         Callbacks will be triggered if :attr:`eventson` is True.
         """
-        if 0 > index >= len(self.labels):
-            raise ValueError("Invalid RadioButton index: %d" % index)
+        if index not in range(len(self.labels)):
+            raise ValueError(f'Invalid RadioButton index: {index}')
 
         self.value_selected = self.labels[index].get_text()
 

From da48bcd796ab8f94b0c84e2f5821303f6ee788e8 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 11 Aug 2020 20:37:39 -0400
Subject: [PATCH 2/4] Deprecated some internal Widget attributes.

---
 .../deprecations/18226-ES.rst                 |  12 ++
 lib/matplotlib/widgets.py                     | 146 ++++++++++++------
 2 files changed, 115 insertions(+), 43 deletions(-)
 create mode 100644 doc/api/next_api_changes/deprecations/18226-ES.rst

diff --git a/doc/api/next_api_changes/deprecations/18226-ES.rst b/doc/api/next_api_changes/deprecations/18226-ES.rst
new file mode 100644
index 000000000000..ad85203d7876
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/18226-ES.rst
@@ -0,0 +1,12 @@
+Widget class internals
+~~~~~~~~~~~~~~~~~~~~~~
+
+Several `.widgets.Widget` class internals have been privatized and deprecated:
+
+* ``AxesWidget.cids``
+* ``Button.cnt`` and ``Button.observers``
+* ``CheckButtons.cnt`` and ``CheckButtons.observers``
+* ``RadioButtons.cnt`` and ``RadioButtons.observers``
+* ``Slider.cnt`` and ``Slider.observers``
+* ``TextBox.cnt``, ``TextBox.change_observers`` and
+  ``TextBox.submit_observers``
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
index 1ce7061dbed6..fce2ae39ad0d 100644
--- a/lib/matplotlib/widgets.py
+++ b/lib/matplotlib/widgets.py
@@ -112,7 +112,12 @@ class AxesWidget(Widget):
     def __init__(self, ax):
         self.ax = ax
         self.canvas = ax.figure.canvas
-        self.cids = []
+        self._cids = []
+
+    @cbook.deprecated("3.4")
+    @property
+    def cids(self):
+        return self._cids
 
     def connect_event(self, event, callback):
         """
@@ -122,11 +127,11 @@ def connect_event(self, event, callback):
         function stores callback ids for later clean up.
         """
         cid = self.canvas.mpl_connect(event, callback)
-        self.cids.append(cid)
+        self._cids.append(cid)
 
     def disconnect_events(self):
         """Disconnect all events created by this widget."""
-        for c in self.cids:
+        for c in self._cids:
             self.canvas.mpl_disconnect(c)
 
 
@@ -175,8 +180,8 @@ def __init__(self, ax, label, image=None,
                              horizontalalignment='center',
                              transform=ax.transAxes)
 
-        self.cnt = 0
-        self.observers = {}
+        self._cnt = 0
+        self._observers = {}
 
         self.connect_event('button_press_event', self._click)
         self.connect_event('button_release_event', self._release)
@@ -188,6 +193,16 @@ def __init__(self, ax, label, image=None,
         self.color = color
         self.hovercolor = hovercolor
 
+    @cbook.deprecated("3.4")
+    @property
+    def cnt(self):
+        return self._cnt
+
+    @cbook.deprecated("3.4")
+    @property
+    def observers(self):
+        return self._observers
+
     def _click(self, event):
         if (self.ignore(event)
                 or event.inaxes != self.ax
@@ -204,7 +219,7 @@ def _release(self, event):
         if (not self.eventson
                 or event.inaxes != self.ax):
             return
-        for cid, func in self.observers.items():
+        for cid, func in self._observers.items():
             func(event)
 
     def _motion(self, event):
@@ -222,15 +237,15 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self.cnt
-        self.observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._observers[cid] = func
+        self._cnt += 1
         return cid
 
     def disconnect(self, cid):
         """Remove the callback function with connection id *cid*."""
         try:
-            del self.observers[cid]
+            del self._observers[cid]
         except KeyError:
             pass
 
@@ -382,11 +397,21 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
                                    verticalalignment='center',
                                    horizontalalignment='left')
 
-        self.cnt = 0
-        self.observers = {}
+        self._cnt = 0
+        self._observers = {}
 
         self.set_val(valinit)
 
+    @cbook.deprecated("3.4")
+    @property
+    def cnt(self):
+        return self._cnt
+
+    @cbook.deprecated("3.4")
+    @property
+    def observers(self):
+        return self._observers
+
     def _value_in_bounds(self, val):
         """Makes sure *val* is with given bounds."""
         if self.valstep:
@@ -469,7 +494,7 @@ def set_val(self, val):
         self.val = val
         if not self.eventson:
             return
-        for cid, func in self.observers.items():
+        for cid, func in self._observers.items():
             func(val)
 
     def on_changed(self, func):
@@ -488,9 +513,9 @@ def on_changed(self, func):
         int
             Connection id (which can be used to disconnect *func*)
         """
-        cid = self.cnt
-        self.observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._observers[cid] = func
+        self._cnt += 1
         return cid
 
     def disconnect(self, cid):
@@ -503,7 +528,7 @@ def disconnect(self, cid):
             Connection id of the observer to be removed
         """
         try:
-            del self.observers[cid]
+            del self._observers[cid]
         except KeyError:
             pass
 
@@ -600,8 +625,18 @@ def __init__(self, ax, labels, actives=None):
 
         self.connect_event('button_press_event', self._clicked)
 
-        self.cnt = 0
-        self.observers = {}
+        self._cnt = 0
+        self._observers = {}
+
+    @cbook.deprecated("3.4")
+    @property
+    def cnt(self):
+        return self._cnt
+
+    @cbook.deprecated("3.4")
+    @property
+    def observers(self):
+        return self._observers
 
     def _clicked(self, event):
         if self.ignore(event) or event.button != 1 or event.inaxes != self.ax:
@@ -640,7 +675,7 @@ def set_active(self, index):
 
         if not self.eventson:
             return
-        for cid, func in self.observers.items():
+        for cid, func in self._observers.items():
             func(self.labels[index].get_text())
 
     def get_status(self):
@@ -655,15 +690,15 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self.cnt
-        self.observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._observers[cid] = func
+        self._cnt += 1
         return cid
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
         try:
-            del self.observers[cid]
+            del self._observers[cid]
         except KeyError:
             pass
 
@@ -725,9 +760,9 @@ def __init__(self, ax, label, initial='',
             self.DIST_FROM_LEFT, 0.5, initial, transform=self.ax.transAxes,
             verticalalignment='center', horizontalalignment='left')
 
-        self.cnt = 0
-        self.change_observers = {}
-        self.submit_observers = {}
+        self._cnt = 0
+        self._change_observers = {}
+        self._submit_observers = {}
 
         ax.set(
             xlim=(0, 1), ylim=(0, 1),  # s.t. cursor appears from first click.
@@ -750,6 +785,21 @@ def __init__(self, ax, label, initial='',
 
         self.capturekeystrokes = False
 
+    @cbook.deprecated("3.4")
+    @property
+    def cnt(self):
+        return self._cnt
+
+    @cbook.deprecated("3.4")
+    @property
+    def change_observers(self):
+        return self._change_observers
+
+    @cbook.deprecated("3.4")
+    @property
+    def submit_observers(self):
+        return self._submit_observers
+
     @property
     def text(self):
         return self.text_disp.get_text()
@@ -780,7 +830,7 @@ def _rendercursor(self):
 
     def _notify_submit_observers(self):
         if self.eventson:
-            for cid, func in self.submit_observers.items():
+            for cid, func in self._submit_observers.items():
                 func(self.text)
 
     def _release(self, event):
@@ -836,7 +886,7 @@ def set_val(self, val):
 
     def _notify_change_observers(self):
         if self.eventson:
-            for cid, func in self.change_observers.items():
+            for cid, func in self._change_observers.items():
                 func(self.text)
 
     def begin_typing(self, x):
@@ -918,9 +968,9 @@ def on_text_change(self, func):
 
         A connection id is returned which can be used to disconnect.
         """
-        cid = self.cnt
-        self.change_observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._change_observers[cid] = func
+        self._cnt += 1
         return cid
 
     def on_submit(self, func):
@@ -930,14 +980,14 @@ def on_submit(self, func):
 
         A connection id is returned which can be used to disconnect.
         """
-        cid = self.cnt
-        self.submit_observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._submit_observers[cid] = func
+        self._cnt += 1
         return cid
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
-        for reg in [self.change_observers, self.submit_observers]:
+        for reg in [self._change_observers, self._submit_observers]:
             try:
                 del reg[cid]
             except KeyError:
@@ -1022,8 +1072,18 @@ def __init__(self, ax, labels, active=0, activecolor='blue'):
 
         self.connect_event('button_press_event', self._clicked)
 
-        self.cnt = 0
-        self.observers = {}
+        self._cnt = 0
+        self._observers = {}
+
+    @cbook.deprecated("3.4")
+    @property
+    def cnt(self):
+        return self._cnt
+
+    @cbook.deprecated("3.4")
+    @property
+    def observers(self):
+        return self._observers
 
     def _clicked(self, event):
         if self.ignore(event) or event.button != 1 or event.inaxes != self.ax:
@@ -1061,7 +1121,7 @@ def set_active(self, index):
 
         if not self.eventson:
             return
-        for cid, func in self.observers.items():
+        for cid, func in self._observers.items():
             func(self.labels[index].get_text())
 
     def on_clicked(self, func):
@@ -1070,15 +1130,15 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self.cnt
-        self.observers[cid] = func
-        self.cnt += 1
+        cid = self._cnt
+        self._observers[cid] = func
+        self._cnt += 1
         return cid
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
         try:
-            del self.observers[cid]
+            del self._observers[cid]
         except KeyError:
             pass
 

From b9d9049ff8a55568b480e7b44abacc1cc7375602 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 11 Aug 2020 21:02:39 -0400
Subject: [PATCH 3/4] Use CallbackRegistry for all Widget event observers.

This simplifies processing, fixes memory leaks with weak references, and
fixes bugs like being unable to disconnect a callback in its own code.
---
 .../next_api_changes/behavior/18226-ES.rst    |  10 ++
 lib/matplotlib/widgets.py                     | 139 ++++++------------
 2 files changed, 56 insertions(+), 93 deletions(-)
 create mode 100644 doc/api/next_api_changes/behavior/18226-ES.rst

diff --git a/doc/api/next_api_changes/behavior/18226-ES.rst b/doc/api/next_api_changes/behavior/18226-ES.rst
new file mode 100644
index 000000000000..c6247737f662
--- /dev/null
+++ b/doc/api/next_api_changes/behavior/18226-ES.rst
@@ -0,0 +1,10 @@
+Widgets use ``CallbackRegistry`` to save callbacks
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+`.Widget`\s with event observers now use a `.CallbackRegistry` for storing
+callbacks. This is consistent with canvas event callbacks, and fixes some bugs
+in widget callback handling.
+
+Due to this change, callback methods are now stored as weak references, which
+means you must keep a reference to the associated object. Otherwise it may be
+garbage collected.
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
index fce2ae39ad0d..95314722c649 100644
--- a/lib/matplotlib/widgets.py
+++ b/lib/matplotlib/widgets.py
@@ -180,8 +180,7 @@ def __init__(self, ax, label, image=None,
                              horizontalalignment='center',
                              transform=ax.transAxes)
 
-        self._cnt = 0
-        self._observers = {}
+        self._observers = cbook.CallbackRegistry()
 
         self.connect_event('button_press_event', self._click)
         self.connect_event('button_release_event', self._release)
@@ -196,12 +195,13 @@ def __init__(self, ax, label, image=None,
     @cbook.deprecated("3.4")
     @property
     def cnt(self):
-        return self._cnt
+        # Not real, but close enough.
+        return len(self._observers.callbacks['clicked'])
 
     @cbook.deprecated("3.4")
     @property
     def observers(self):
-        return self._observers
+        return self._observers.callbacks['clicked']
 
     def _click(self, event):
         if (self.ignore(event)
@@ -219,8 +219,7 @@ def _release(self, event):
         if (not self.eventson
                 or event.inaxes != self.ax):
             return
-        for cid, func in self._observers.items():
-            func(event)
+        self._observers.process('clicked', event)
 
     def _motion(self, event):
         if self.ignore(event):
@@ -237,17 +236,11 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self._cnt
-        self._observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('clicked', func)
 
     def disconnect(self, cid):
         """Remove the callback function with connection id *cid*."""
-        try:
-            del self._observers[cid]
-        except KeyError:
-            pass
+        self._observers.disconnect(cid)
 
 
 class Slider(AxesWidget):
@@ -397,20 +390,20 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
                                    verticalalignment='center',
                                    horizontalalignment='left')
 
-        self._cnt = 0
-        self._observers = {}
+        self._observers = cbook.CallbackRegistry()
 
         self.set_val(valinit)
 
     @cbook.deprecated("3.4")
     @property
     def cnt(self):
-        return self._cnt
+        # Not real, but close enough.
+        return len(self._observers.callbacks['changed'])
 
     @cbook.deprecated("3.4")
     @property
     def observers(self):
-        return self._observers
+        return self._observers.callbacks['changed']
 
     def _value_in_bounds(self, val):
         """Makes sure *val* is with given bounds."""
@@ -494,8 +487,7 @@ def set_val(self, val):
         self.val = val
         if not self.eventson:
             return
-        for cid, func in self._observers.items():
-            func(val)
+        self._observers.process('changed', val)
 
     def on_changed(self, func):
         """
@@ -513,10 +505,7 @@ def on_changed(self, func):
         int
             Connection id (which can be used to disconnect *func*)
         """
-        cid = self._cnt
-        self._observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('changed', func)
 
     def disconnect(self, cid):
         """
@@ -527,10 +516,7 @@ def disconnect(self, cid):
         cid : int
             Connection id of the observer to be removed
         """
-        try:
-            del self._observers[cid]
-        except KeyError:
-            pass
+        self._observers.disconnect(cid)
 
     def reset(self):
         """Reset the slider to the initial value"""
@@ -625,18 +611,18 @@ def __init__(self, ax, labels, actives=None):
 
         self.connect_event('button_press_event', self._clicked)
 
-        self._cnt = 0
-        self._observers = {}
+        self._observers = cbook.CallbackRegistry()
 
     @cbook.deprecated("3.4")
     @property
     def cnt(self):
-        return self._cnt
+        # Not real, but close enough.
+        return len(self._observers.callbacks['clicked'])
 
     @cbook.deprecated("3.4")
     @property
     def observers(self):
-        return self._observers
+        return self._observers.callbacks['clicked']
 
     def _clicked(self, event):
         if self.ignore(event) or event.button != 1 or event.inaxes != self.ax:
@@ -675,8 +661,7 @@ def set_active(self, index):
 
         if not self.eventson:
             return
-        for cid, func in self._observers.items():
-            func(self.labels[index].get_text())
+        self._observers.process('clicked', self.labels[index].get_text())
 
     def get_status(self):
         """
@@ -690,17 +675,11 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self._cnt
-        self._observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('clicked', func)
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
-        try:
-            del self._observers[cid]
-        except KeyError:
-            pass
+        self._observers.disconnect(cid)
 
 
 class TextBox(AxesWidget):
@@ -760,9 +739,7 @@ def __init__(self, ax, label, initial='',
             self.DIST_FROM_LEFT, 0.5, initial, transform=self.ax.transAxes,
             verticalalignment='center', horizontalalignment='left')
 
-        self._cnt = 0
-        self._change_observers = {}
-        self._submit_observers = {}
+        self._observers = cbook.CallbackRegistry()
 
         ax.set(
             xlim=(0, 1), ylim=(0, 1),  # s.t. cursor appears from first click.
@@ -788,17 +765,18 @@ def __init__(self, ax, label, initial='',
     @cbook.deprecated("3.4")
     @property
     def cnt(self):
-        return self._cnt
+        # Not real, but close enough.
+        return sum(len(d) for d in self._observers.callbacks.values())
 
     @cbook.deprecated("3.4")
     @property
     def change_observers(self):
-        return self._change_observers
+        return self._observers.callbacks['change']
 
     @cbook.deprecated("3.4")
     @property
     def submit_observers(self):
-        return self._submit_observers
+        return self._observers.callbacks['submit']
 
     @property
     def text(self):
@@ -828,11 +806,6 @@ def _rendercursor(self):
 
         self.ax.figure.canvas.draw()
 
-    def _notify_submit_observers(self):
-        if self.eventson:
-            for cid, func in self._submit_observers.items():
-                func(self.text)
-
     def _release(self, event):
         if self.ignore(event):
             return
@@ -871,9 +844,10 @@ def _keypress(self, event):
                             text[self.cursor_index + 1:])
             self.text_disp.set_text(text)
             self._rendercursor()
-            self._notify_change_observers()
-            if key == "enter":
-                self._notify_submit_observers()
+            if self.eventson:
+                self._observers.process('change', self.text)
+                if key == "enter":
+                    self._observers.process('submit', self.text)
 
     def set_val(self, val):
         newval = str(val)
@@ -881,13 +855,9 @@ def set_val(self, val):
             return
         self.text_disp.set_text(newval)
         self._rendercursor()
-        self._notify_change_observers()
-        self._notify_submit_observers()
-
-    def _notify_change_observers(self):
         if self.eventson:
-            for cid, func in self._change_observers.items():
-                func(self.text)
+            self._observers.process('change', self.text)
+            self._observers.process('submit', self.text)
 
     def begin_typing(self, x):
         self.capturekeystrokes = True
@@ -920,10 +890,10 @@ def stop_typing(self):
         self.capturekeystrokes = False
         self.cursor.set_visible(False)
         self.ax.figure.canvas.draw()
-        if notifysubmit:
-            # Because _notify_submit_observers might throw an error in the
-            # user's code, only call it once we've already done our cleanup.
-            self._notify_submit_observers()
+        if notifysubmit and self.eventson:
+            # Because process() might throw an error in the user's code, only
+            # call it once we've already done our cleanup.
+            self._observers.process('submit', self.text)
 
     def position_cursor(self, x):
         # now, we have to figure out where the cursor goes.
@@ -968,10 +938,7 @@ def on_text_change(self, func):
 
         A connection id is returned which can be used to disconnect.
         """
-        cid = self._cnt
-        self._change_observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('change', func)
 
     def on_submit(self, func):
         """
@@ -980,18 +947,11 @@ def on_submit(self, func):
 
         A connection id is returned which can be used to disconnect.
         """
-        cid = self._cnt
-        self._submit_observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('submit', func)
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
-        for reg in [self._change_observers, self._submit_observers]:
-            try:
-                del reg[cid]
-            except KeyError:
-                pass
+        self._observers.disconnect(cid)
 
 
 class RadioButtons(AxesWidget):
@@ -1072,18 +1032,18 @@ def __init__(self, ax, labels, active=0, activecolor='blue'):
 
         self.connect_event('button_press_event', self._clicked)
 
-        self._cnt = 0
-        self._observers = {}
+        self._observers = cbook.CallbackRegistry()
 
     @cbook.deprecated("3.4")
     @property
     def cnt(self):
-        return self._cnt
+        # Not real, but close enough.
+        return len(self._observers.callbacks['clicked'])
 
     @cbook.deprecated("3.4")
     @property
     def observers(self):
-        return self._observers
+        return self._observers.callbacks['clicked']
 
     def _clicked(self, event):
         if self.ignore(event) or event.button != 1 or event.inaxes != self.ax:
@@ -1121,8 +1081,7 @@ def set_active(self, index):
 
         if not self.eventson:
             return
-        for cid, func in self._observers.items():
-            func(self.labels[index].get_text())
+        self._observers.process('clicked', self.labels[index].get_text())
 
     def on_clicked(self, func):
         """
@@ -1130,17 +1089,11 @@ def on_clicked(self, func):
 
         Returns a connection id, which can be used to disconnect the callback.
         """
-        cid = self._cnt
-        self._observers[cid] = func
-        self._cnt += 1
-        return cid
+        return self._observers.connect('clicked', func)
 
     def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
-        try:
-            del self._observers[cid]
-        except KeyError:
-            pass
+        self._observers.disconnect(cid)
 
 
 class SubplotTool(Widget):

From ae888ca7560079595a9936acfcf9b7d8ea49e561 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 11 Aug 2020 21:17:52 -0400
Subject: [PATCH 4/4] Shorten some conditions in widgets.

---
 lib/matplotlib/widgets.py | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
index 95314722c649..ee0711a8edd4 100644
--- a/lib/matplotlib/widgets.py
+++ b/lib/matplotlib/widgets.py
@@ -204,22 +204,17 @@ def observers(self):
         return self._observers.callbacks['clicked']
 
     def _click(self, event):
-        if (self.ignore(event)
-                or event.inaxes != self.ax
-                or not self.eventson):
+        if self.ignore(event) or event.inaxes != self.ax or not self.eventson:
             return
         if event.canvas.mouse_grabber != self.ax:
             event.canvas.grab_mouse(self.ax)
 
     def _release(self, event):
-        if (self.ignore(event)
-                or event.canvas.mouse_grabber != self.ax):
+        if self.ignore(event) or event.canvas.mouse_grabber != self.ax:
             return
         event.canvas.release_mouse(self.ax)
-        if (not self.eventson
-                or event.inaxes != self.ax):
-            return
-        self._observers.process('clicked', event)
+        if self.eventson and event.inaxes == self.ax:
+            self._observers.process('clicked', event)
 
     def _motion(self, event):
         if self.ignore(event):
@@ -485,9 +480,8 @@ def set_val(self, val):
         if self.drawon:
             self.ax.figure.canvas.draw_idle()
         self.val = val
-        if not self.eventson:
-            return
-        self._observers.process('changed', val)
+        if self.eventson:
+            self._observers.process('changed', val)
 
     def on_changed(self, func):
         """
@@ -659,9 +653,8 @@ def set_active(self, index):
         if self.drawon:
             self.ax.figure.canvas.draw()
 
-        if not self.eventson:
-            return
-        self._observers.process('clicked', self.labels[index].get_text())
+        if self.eventson:
+            self._observers.process('clicked', self.labels[index].get_text())
 
     def get_status(self):
         """
@@ -1079,9 +1072,8 @@ def set_active(self, index):
         if self.drawon:
             self.ax.figure.canvas.draw()
 
-        if not self.eventson:
-            return
-        self._observers.process('clicked', self.labels[index].get_text())
+        if self.eventson:
+            self._observers.process('clicked', self.labels[index].get_text())
 
     def on_clicked(self, func):
         """