Revert my changes, this is a much bigger job.

src/allmydata/test/test_python2_regressions.py

@@ -1,37 +1,31 @@
 """
 Tests to check for Python2 regressions
 """
-
-from types import (
-    ClassType,
-)
-
 from twisted.trial import unittest
 from twisted.python.modules import getModule
 
-def is_classic_class(obj):
-    """check an object being a classic class"""
-    # issubclass() is a great idea but it blows up if the first argument is
-    # not a class.  So ... less than completely useful.
-    return type(obj) is ClassType
-
-def defined_here(obj, where):
-    return obj.__module__ == where
-
 class PythonTwoRegressions(unittest.TestCase):
     """
     A test class to hold Python2 regression tests.
     """
-    def test_new_style_class(self):
+
+    def is_new_style(self, cls):
+        """check for being a new-style class"""
+        # another test could be: issubclass(value, type)
+        has_class_attr = hasattr(cls, '__class__')
+        dict_or_slots = '__dict__' in dir(cls) or hasattr(cls, '__slots__')
+        return has_class_attr and dict_or_slots
+
+    def test_old_style_class(self):
         """
-        All classes defined by Tahoe-LAFS are new-style.
+        Check if all classes are new-style classes
         """
         for mod in getModule("allmydata").walkModules():
-            # Cannot iterate attributes of unloaded modules.
-            mod.load()
             for attr in mod.iterAttributes():
                 value = attr.load()
-                self.assertFalse(
-                    is_classic_class(value) and defined_here(value, mod.name),
-                    "{} appears to be a classic class".format(attr.name),
-                )
+                if isinstance(value, str):
+                    # apparently strings are note a new-style class (in Python 2.7)
+                    # so we skip testing them
+                    return
+                self.assertTrue(self.is_new_style(value),
+                                "{} does not seem to be a new-style class".format(attr.name))