Create rectangles/lines when the other is accessed

The rectangles/lines attributes exist for backcompat and the expectation
would be that when either one of them is accessed, the other would also
be set in the way the older method does. So, whenever either of the
property is accessed for the first time, it also sets the other
property. This way, it maintains consistency with the old API.

Author: chahak13

doc/api/next_api_changes/deprecations/24474_CM.rst

@@ -0,0 +1,3 @@
+``CheckButtons``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+``CheckButtons.rectangles`` and ``CheckButtons.lines`` are deprecated.  (``CheckButtons`` now draws itself using `~.Axes.scatter`.)

lib/matplotlib/tests/test_widgets.py

@@ -1011,8 +1011,6 @@ def test_check_radio_buttons_image():
     with pytest.warns(DeprecationWarning):
         # Trigger old-style Rectangle check boxes
         cb.rectangles
-    with pytest.warns(DeprecationWarning):
-        cb.lines
 
 
 @check_figures_equal(extensions=["png"])

lib/matplotlib/widgets.py

@@ -1132,6 +1132,9 @@ def rectangles(self):
             self._squares.set_visible(False)
             for rectangle in rectangles:
                 self.ax.add_patch(rectangle)
+        if not hasattr(self, "_lines"):
+            with _api.suppress_matplotlib_deprecation_warning():
+                _ = self.lines
         return self._rectangles
 
     @_api.deprecated("3.7")
@@ -1157,6 +1160,9 @@ def lines(self):
                 self._lines.append((l1, l2))
                 self.ax.add_patch(l1)
                 self.ax.add_patch(l2)
+        if not hasattr(self, "_rectangles"):
+            with _api.suppress_matplotlib_deprecation_warning():
+                _ = self.rectangles
         return self._lines