Merge pull request #7914 from anntzer/callbackregistry-unpickling

NelleV · NelleV · commit 5813452e876d · 2017-01-23T23:38:04.000-08:00
Fix unpickling of CallbackRegistry on Py2.
diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -481,13 +481,18 @@ 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
 
@@ -331,6 +332,10 @@ def test_callback_complete(self):
     def dummy(self):
         pass
 
+    def test_pickling(self):
+        assert hasattr(pickle.loads(pickle.dumps(cbook.CallbackRegistry())),
+                       "callbacks")
+
 
 def _kwarg_norm_helper(inp, expected, kwargs_to_norm, warn_count=0):
 
