code: def subclasses(self, sort_by=None, reverse=False):
          
          l = list()
          for attr, _ in self.Subclasses(sort_by, reverse):
              value = getattr(self, attr)
              l.append((attr, value))
          return l
docs: Get all nested Constant class instance and it's name pair.
  
          :param sort_by: the attribute name used for sorting.
          :param reverse: if True, return in descend order.
          :returns: [(attr, value),...] pairs.
  
          ::
  
              >>> class MyClass(Constant):
              ...     a = 1 # non-class attributre
              ...     b = 2 # non-class attributre
              ...
              ...     class C(Constant):
              ...         pass
              ...
              ...     class D(Constant):
              ...         pass
  
              >>> my_class = MyClass()
              >>> my_class.subclasses()
              [("C", my_class.C), ("D", my_class.D)]
  
          .. versionadded:: 0.0.4