Merge pull request matplotlib#16824 from anntzer/qtoolbarparent

Deprecate NavigationToolbar2QT.parent.

Author: timhoffm

doc/api/next_api_changes/deprecations.rst

@@ -370,3 +370,9 @@ mathtext ``Glue`` helper classes
 The ``Fil``, ``Fill``, ``Filll``, ``NegFil``, ``NegFill``, ``NegFilll``, and
 ``SsGlue`` classes in the :mod:`matplotlib.mathtext` module are deprecated.
 As an alternative, directly construct glue instances with ``Glue("fil")``, etc.
+
+NavigationToolbar2QT.parent
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This attribute is deprecated.  In order to access the parent window, use
+``toolbar.canvas.parent()``.  Once the deprecation period is elapsed, it will
+also be accessible as ``toolbar.parent()``.

lib/matplotlib/backends/backend_qt5.py

@@ -660,14 +660,19 @@ class NavigationToolbar2QT(NavigationToolbar2, QtWidgets.QToolBar):
     def __init__(self, canvas, parent, coordinates=True):
         """coordinates: should we show the coordinates on the right?"""
         self.canvas = canvas
-        self.parent = parent
+        self._parent = parent
         self.coordinates = coordinates
         self._actions = {}
         """A mapping of toolitem method names to their QActions"""
 
         QtWidgets.QToolBar.__init__(self, parent)
         NavigationToolbar2.__init__(self, canvas)
 
+    @cbook.deprecated("3.3", alternative="self.canvas.parent()")
+    @property
+    def parent(self):
+        return self._parent
+
     def _icon(self, name, color=None):
         if is_pyqt5():
             name = name.replace('.png', '_large.png')
@@ -718,7 +723,7 @@ def edit_parameters(self):
         axes = self.canvas.figure.get_axes()
         if not axes:
             QtWidgets.QMessageBox.warning(
-                self.parent, "Error", "There are no axes to edit.")
+                self.canvas.parent(), "Error", "There are no axes to edit.")
             return
         elif len(axes) == 1:
             ax, = axes
@@ -735,7 +740,8 @@ def edit_parameters(self):
                 if titles[i] in duplicate_titles:
                     titles[i] += f" (id: {id(ax):#x})"  # Deduplicate titles.
             item, ok = QtWidgets.QInputDialog.getItem(
-                self.parent, 'Customize', 'Select axes:', titles, 0, False)
+                self.canvas.parent(),
+                'Customize', 'Select axes:', titles, 0, False)
             if not ok:
                 return
             ax = axes[titles.index(item)]