Fix TypeError when accessing TreeWalk().__dict__ (#137)

Fixes #136

astor/tree_walk.py

@@ -30,6 +30,9 @@ class MetaFlatten(type):
             if base not in newbases:
                 newdict.update(vars(base))
         newdict.update(clsdict)
+        # These are class-bound, we should let Python recreate them.
+        newdict.pop('__dict__', None)
+        newdict.pop('__weakref__', None)
         # Delegate the real work to type
         return type.__new__(clstype, name, newbases, newdict)
 

docs/changelog.rst

@@ -53,6 +53,13 @@ Bug fixes
 .. _`Issue 127`: https://github.com/berkerpeksag/astor/issues/127
 .. _`PR 130`: https://github.com/berkerpeksag/astor/pull/130
 
+* Fixed :class:`astor.tree_walk.TreeWalk` when attempting to access attributes
+  created by Python's type system (such as ``__dict__`` and ``__weakref__``)
+  (Reported and fixed by esupoff in `Issue 136`_ and `PR 137`_.)
+  
+.. _`Issue 136`: https://github.com/berkerpeksag/astor/issues/136
+.. _`PR 137`: https://github.com/berkerpeksag/astor/pull/137
+
 0.7.1 - 2018-07-06
 ------------------
 

tests/test_misc.py

@@ -64,5 +64,17 @@ class FastCompareTestCase(unittest.TestCase):
         check('a = 3 - (3, 4, 5)', 'a = 3 - (3, 4, 6)')
 
 
+class TreeWalkTestCase(unittest.TestCase):
+
+    def test_auto_generated_attributes(self):
+        # See #136 for more details.
+        treewalk = astor.TreeWalk()
+        self.assertIsInstance(treewalk.__dict__, dict)
+        # Check that the inital state of the instance is empty.
+        self.assertEqual(treewalk.__dict__['nodestack'], [])
+        self.assertEqual(treewalk.__dict__['pre_handlers'], {})
+        self.assertEqual(treewalk.__dict__['post_handlers'], {})
+
+
 if __name__ == '__main__':
     unittest.main()