MNT: py312 deprecates pickling objects in itertools

Author: tacaswell

lib/matplotlib/cbook.py

@@ -192,9 +192,11 @@ def __getstate__(self):
                           for s, d in self.callbacks.items()},
             # It is simpler to reconstruct this from callbacks in __setstate__.
             "_func_cid_map": None,
+            "_cid_gen": next(self._cid_gen)
         }
 
     def __setstate__(self, state):
+        cid_count = state.pop('_cid_gen')
         vars(self).update(state)
         self.callbacks = {
             s: {cid: _weak_or_strong_ref(func, self._remove_proxy)
@@ -203,6 +205,7 @@ def __setstate__(self, state):
         self._func_cid_map = {
             s: {proxy: cid for cid, proxy in d.items()}
             for s, d in self.callbacks.items()}
+        self._cid_gen = itertools.count(cid_count)
 
     def connect(self, signal, func):
         """Register *func* to be called when signal *signal* is generated."""

lib/matplotlib/tests/test_cbook.py

@@ -209,6 +209,13 @@ def is_not_empty(self):
         assert self.callbacks._func_cid_map != {}
         assert self.callbacks.callbacks != {}
 
+    def test_cid_restore(self):
+        cb = cbook.CallbackRegistry()
+        cb.connect('a', lambda: None)
+        cb2 = pickle.loads(pickle.dumps(cb))
+        cid = cb2.connect('c', lambda: None)
+        assert cid == 1
+
     @pytest.mark.parametrize('pickle', [True, False])
     def test_callback_complete(self, pickle):
         # ensure we start with an empty registry