when mangling private attributes in Python classes, leading underscores must...

when mangling private attributes in Python classes, leading underscores must be removed from the class name before mangling

Cython/Compiler/Symtab.py

@@ -1636,7 +1636,7 @@ class PyClassScope(ClassScope):
 
     def mangle_special_name(self, name):
         if name and name.startswith('__') and not name.endswith('__'):
-            name = EncodedString('_%s%s' % (self.class_name, name))
+            name = EncodedString('_%s%s' % (self.class_name.lstrip('_'), name))
         return name
 
     def lookup_here(self, name):

tests/run/methodmangling_T5.py

@@ -76,3 +76,20 @@ class CyTestSub(CyTest):
         def get(o):
             return o._CyTest__x, o._CyTestSub__y, o.__y, o.__private()
         return get(self)
+
+class _UnderscoreTest(object):
+    """
+    >>> ut = _UnderscoreTest()
+    >>> '__x' in dir(ut)
+    False
+    >>> '_UnderscoreTest__x' in dir(ut)
+    True
+    >>> ut._UnderscoreTest__x
+    1
+    >>> ut.get()
+    1
+    """
+    __x = 1
+
+    def get(self):
+        return self.__x