add try in __eq__ for operator

pymath/calculus/operator/operator.py

@@ -209,7 +209,10 @@ class Operator():
 
     def __eq__(self, op2):
         """ op1 == op2 """
-        return self.name == op2.name and self.arity == op2.arity
+        try:
+            return self.name == op2.name and self.arity == op2.arity
+        except AttributeError:
+            return False
 
 def save_mainOp(obj, mainOp):
     """Create a temporary class build over built-in type to stock the main operation of a calculus