Deprecate ScalarMappable.check_update and associated machinery.

It's a rather complex machinery that's ultimately just used by
Collection to know whether the alpha array has been updated so that the
value-to-rgba mapping needs to be updated.  Users can't connect to it to
know whether the mapped values have been updated, and they can't even
use it to check whether the *alpha* values have been updated because
this unsets the marker and thus would mess up Collection's own use of
it.  For now, just deprecate its public use to ultimately make it
private and perhaps replace it later by something less brittle (e.g.,
normal a normal callback registry).

Author: anntzer

doc/api/api_changes_3.3/deprecations.rst

@@ -450,3 +450,8 @@ needed.
 The associated helper methods ``NavigationToolbar2.draw()`` and
 ``ToolViewsPositions.refresh_locators()`` are deprecated, and should be
 replaced by calls to ``draw_idle()`` on the corresponding canvas.
+
+`.ScalarMappable` checkers
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+The ``add_checker`` and ``check_update`` methods and ``update_dict`` attribute
+of `.ScalarMappable` are deprecated.

lib/matplotlib/cm.py

@@ -177,7 +177,7 @@ def __init__(self, norm=None, cmap=None):
         #: The last colorbar associated with this ScalarMappable. May be None.
         self.colorbar = None
         self.callbacksSM = cbook.CallbackRegistry()
-        self.update_dict = {'array': False}
+        self._update_dict = {'array': False}
 
     def _scale_norm(self, norm, vmin, vmax):
         """
@@ -279,7 +279,7 @@ def set_array(self, A):
         A : ndarray
         """
         self._A = A
-        self.update_dict['array'] = True
+        self._update_dict['array'] = True
 
     def get_array(self):
         """Return the data array."""
@@ -386,30 +386,39 @@ def autoscale_None(self):
         self.norm.autoscale_None(self._A)
         self.changed()
 
-    def add_checker(self, checker):
+    def _add_checker(self, checker):
         """
         Add an entry to a dictionary of boolean flags
         that are set to True when the mappable is changed.
         """
-        self.update_dict[checker] = False
+        self._update_dict[checker] = False
 
-    def check_update(self, checker):
-        """
-        If mappable has changed since the last check,
-        return True; else return False
-        """
-        if self.update_dict[checker]:
-            self.update_dict[checker] = False
+    def _check_update(self, checker):
+        """Return whether mappable has changed since the last check."""
+        if self._update_dict[checker]:
+            self._update_dict[checker] = False
             return True
         return False
 
     def changed(self):
         """
         Call this whenever the mappable is changed to notify all the
-        callbackSM listeners to the 'changed' signal
+        callbackSM listeners to the 'changed' signal.
         """
         self.callbacksSM.process('changed', self)
-
-        for key in self.update_dict:
-            self.update_dict[key] = True
+        for key in self._update_dict:
+            self._update_dict[key] = True
         self.stale = True
+
+    @cbook.deprecated("3.3")
+    @property
+    def update_dict(self):
+        return self._update_dict
+
+    @cbook.deprecated("3.3")
+    def add_checker(self, checker):
+        return self._add_checker(checker)
+
+    @cbook.deprecated("3.3")
+    def check_update(self, checker):
+        return self.check_update(checker)

lib/matplotlib/collections.py

@@ -768,7 +768,7 @@ def set_edgecolor(self, c):
     def set_alpha(self, alpha):
         # docstring inherited
         super().set_alpha(alpha)
-        self.update_dict['array'] = True
+        self._update_dict['array'] = True
         self._set_facecolor(self._original_facecolor)
         self._set_edgecolor(self._original_edgecolor)
 
@@ -784,7 +784,7 @@ def update_scalarmappable(self):
             return
         if self._A.ndim > 1:
             raise ValueError('Collections can only map rank 1 arrays')
-        if not self.check_update("array"):
+        if not self._check_update("array"):
             return
         if self._is_filled:
             self._facecolors = self.to_rgba(self._A, self._alpha)
@@ -815,7 +815,7 @@ def update_from(self, other):
         self._A = other._A
         self.norm = other.norm
         self.cmap = other.cmap
-        # self.update_dict = other.update_dict # do we need to copy this? -JJL
+        # do we need to copy self._update_dict? -JJL
         self.stale = True