diff --git a/examples/highfreq/highfreq_ops.py b/examples/highfreq/highfreq_ops.py
index 461c34e6f..66a084f9f 100644
--- a/examples/highfreq/highfreq_ops.py
+++ b/examples/highfreq/highfreq_ops.py
@@ -172,7 +172,7 @@ class Cut(ElemOperator):
     def __init__(self, feature, l=None, r=None):
         self.l = l
         self.r = r
-        if (not self.l is None and self.l <= 0) or (not self.r is None and self.r >= 0):
+        if (self.l is not None and self.l <= 0) or (self.r is not None and self.r >= 0):
             raise ValueError("Cut operator l shoud > 0 and r should < 0")
 
         super(Cut, self).__init__(feature)