250 

   250 

   251     def __eq__(self, other):

   251     def __eq__(self, other):

   252         if hasattr(other, 'expression'):

   252         if hasattr(other, 'expression'):

   253             return self.expression == other.expression

   253             return self.expression == other.expression

   254         return False

   254         return False

   255 

   258 

   256     def __hash__(self):

   259     def __hash__(self):

   257         return hash(self.expression)

   260         return hash(self.expression)

   258 

   261 

   259     def __deepcopy__(self, memo):

   262     def __deepcopy__(self, memo):