Another CPython/pure-python difference is the handling of interning instance...

Another CPython/pure-python difference is the handling of interning instance keys. C has always let non-str values through, but the python implementation raised a TypeError. Correct that and add a test case.

persistent/persistence.py

@@ -329,7 +329,15 @@ class Persistent(object):
                 raise TypeError('No instance dict')
             idict.clear()
             for k, v in inst_dict.items():
-                idict[intern(k)] = v
+                # Normally the keys for instance attributes are interned.
+                # Do that here, but only if it is possible to do so.
+
+                # TODO: On Python 2 codebases that straddle Python3,
+                # and use 'from __future__ import unicode_literals' it's not
+                # unheard of to have unicode objects in the __dict__ by accident.
+                # Should we watch for that and attempt to encode it so it can be
+                # interned?
+                idict[intern(k) if type(k) is str else k] = v
         slotnames = self._slotnames()
         if slotnames:
             for k, v in slots.items():

persistent/tests/test_persistence.py

@@ -948,6 +948,19 @@ class _Persistent_Base(object):
             key2 = list(inst2.__dict__.keys())[0]
             self.assertTrue(key1 is key2)
 
+    def test___setstate___doesnt_fail_on_non_string_keys(self):
+        class Derived(self._getTargetClass()):
+            pass
+        inst1 = Derived()
+        inst1.__setstate__({1: 2})
+        self.assertTrue(1 in inst1.__dict__)
+
+        class MyStr(str):
+            pass
+        mystr = MyStr('mystr')
+        inst1.__setstate__({mystr: 2})
+        self.assertTrue(mystr in inst1.__dict__)
+
     def test___reduce__(self):
         from persistent._compat import copy_reg
         inst = self._makeOne()