Add test case for dir() support and fix Python 2 support

Author: rtzoeller

suitcase/structure.py

@@ -294,7 +294,7 @@ def __setattr__(self, key, value):
         return object.__setattr__(self, key, value)
 
     def __dir__(self):
-        return object.__dir__(self) + [str(k) for k, v in self._sorted_fields]
+        return dir(type(self)) + [str(k) for k, v in self._sorted_fields]
 
     def __iter__(self):
         return iter(self._sorted_fields)

suitcase/test/test_fields.py

@@ -1189,5 +1189,14 @@ def test_unpack_greedy_after(self):
         self.assertEqual(m.last.value, b"Doe")
         self.assertEqual(m.greedy, b"Hello World!")
 
+
+class TestDiscoverableFields(unittest.TestCase):
+    def test_dir(self):
+        m = PascalString16()
+        attrs = dir(m)
+        self.assertTrue("length" in attrs)
+        self.assertTrue("value" in attrs)
+
+
 if __name__ == "__main__":
     unittest.main()