matplotlib · NelleV · Jan 24, 2017 · Jan 22, 2017
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -291,13 +291,18 @@ def __init__(self):
         self._cid = 0
         self._func_cid_map = {}
 
+    # In general, callbacks may not be pickled; thus, we simply recreate an
+    # empty dictionary at unpickling.  In order to ensure that `__setstate__`
+    # (which just defers to `__init__`) is called, `__getstate__` must
+    # return a truthy value (for pickle protocol>=3, i.e. Py3, the
+    # *actual* behavior is that `__setstate__` will be called as long as
+    # `__getstate__` does not return `None`, but this is undocumented -- see
+    # http://bugs.python.org/issue12290).
+
     def __getstate__(self):
-        # We cannot currently pickle the callables in the registry, so
-        # return an empty dictionary.
-        return {}
+        return True
 
     def __setstate__(self, state):
-        # re-initialise an empty callback registry
         self.__init__()
 
     def connect(self, s, func):

diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -1,6 +1,7 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 import itertools
+import pickle
 from weakref import ref
 import warnings
 
@@ -283,6 +284,10 @@ def test_callback_complete(self):
     def dummy(self):
         pass
 
+    def test_pickling(self):
+        assert hasattr(pickle.loads(pickle.dumps(cbook.CallbackRegistry())),
+                       "callbacks")
+
 
 def test_sanitize_sequence():
     d = {'a': 1, 'b': 2, 'c': 3}