Don't set missing history buttons.

efiring · efiring · commit a99a4c773fdc · 2019-05-24T14:17:20.000-10:00
Closes #14318.
diff --git a/lib/matplotlib/backends/backend_gtk3.py b/lib/matplotlib/backends/backend_gtk3.py
@@ -607,8 +607,10 @@ def _get_canvas(self, fig):
     def set_history_buttons(self):
         can_backward = self._nav_stack._pos > 0
         can_forward = self._nav_stack._pos < len(self._nav_stack._elements) - 1
-        self._gtk_ids['Back'].set_sensitive(can_backward)
-        self._gtk_ids['Forward'].set_sensitive(can_forward)
+        if 'Back' in self._gtk_ids:
+            self._gtk_ids['Back'].set_sensitive(can_backward)
+        if 'Forward' in self._gtk_ids:
+            self._gtk_ids['Forward'].set_sensitive(can_forward)
 
 
 @cbook.deprecated("3.1")
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -832,8 +832,10 @@ def save_figure(self, *args):
     def set_history_buttons(self):
         can_backward = self._nav_stack._pos > 0
         can_forward = self._nav_stack._pos < len(self._nav_stack._elements) - 1
-        self._actions['back'].setEnabled(can_backward)
-        self._actions['forward'].setEnabled(can_forward)
+        if 'back' in self._actions:
+            self._actions['back'].setEnabled(can_backward)
+        if 'forward' in self._actions:
+            self._actions['forward'].setEnabled(can_forward)
 
 
 class SubplotToolQt(UiSubplotTool):
diff --git a/lib/matplotlib/backends/backend_wx.py b/lib/matplotlib/backends/backend_wx.py
@@ -1556,8 +1556,10 @@ def set_message(self, s):
     def set_history_buttons(self):
         can_backward = self._nav_stack._pos > 0
         can_forward = self._nav_stack._pos < len(self._nav_stack._elements) - 1
-        self.EnableTool(self.wx_ids['Back'], can_backward)
-        self.EnableTool(self.wx_ids['Forward'], can_forward)
+        if 'Back' in self.wx_ids:
+            self.EnableTool(self.wx_ids['Back'], can_backward)
+        if 'Forward' in self.wx_ids:
+            self.EnableTool(self.wx_ids['Forward'], can_forward)
 
 
 class StatusBarWx(wx.StatusBar):
