backport to 2.13.2

setup.py

@@ -43,7 +43,7 @@ setup(name='DocumentTemplate',
       install_requires=[
           'AccessControl',
           'Acquisition',
-          'ExtensionClass>=4.1a1',
+          'ExtensionClass',
           'RestrictedPython',
           'six',
           'zExceptions',

src/DocumentTemplate/DT_Util.py

@@ -76,6 +76,9 @@ class NotBindable:
 for name, f in list(safe_builtins.items()) + list(utility_builtins.items()):
     if type(f) is functype:
         f = NotBindable(f)
+    # Pyston change: why it happended in Pyston?
+    if name is None or f is None:
+        continue
     setattr(TemplateDict, name, f)
 
 if LIMITED_BUILTINS:

src/DocumentTemplate/security.py

@@ -121,6 +121,9 @@ for name, v in safe_builtins.items():
         v = DT_Util.NotBindable(v)
     if name.startswith('__'):
         continue
+    # Pyston change: why it happened in Pyston?
+    if name is None or v is None:
+        continue
     setattr(DT_Util.TemplateDict, name, v)