Apparently, __getstate__() results are coerced to bool in Python 2

and __setstate__() doesn't run if the state is False.

Ensure that we always return a non-false state (another version bump
here).

loopy/tools.py

@@ -396,12 +396,9 @@ class LazilyUnpicklingDictionary(collections.MutableMapping):
         return iter(self._map)
 
     def __getstate__(self):
-        return dict(
+        return {"_map": dict(
             (key, _PickledObjectWrapper.from_object(val))
-            for key, val in six.iteritems(self._map))
-
-    def __setstate__(self, state):
-        self._map = state
+            for key, val in six.iteritems(self._map))}
 
 # }}}
 

loopy/version.py

@@ -32,4 +32,4 @@ except ImportError:
 else:
     _islpy_version = islpy.version.VERSION_TEXT
 
-DATA_MODEL_VERSION = "v57-islpy%s" % _islpy_version
+DATA_MODEL_VERSION = "v58-islpy%s" % _islpy_version

test/test_misc.py

@@ -97,7 +97,7 @@ class PicklableItem(object):
     flags = {"unpickled": False}
 
     def __getstate__(self):
-        return ()
+        return True
 
     def __setstate__(self, state):
         PicklableItem.flags["unpickled"] = True
@@ -135,6 +135,14 @@ def test_LazilyUnpicklingDictionary():
 
     # }}}
 
+    # {{{ test empty map
+
+    mapping = LazilyUnpicklingDictionary({})
+    mapping = loads(dumps(mapping))
+    assert len(mapping) == 0
+
+    # }}}
+
 
 if __name__ == "__main__":
     if len(sys.argv) > 1: