Compare to None with is/is not

test/functional/mining_prioritisetransaction.py

@@ -84,7 +84,7 @@ class PrioritiseTransactionTest(BitcoinTestFramework):
                 high_fee_tx = x
 
         # Something high-fee should have been mined!
-        assert(high_fee_tx != None)
+        assert(high_fee_tx is not None)
 
         # Add a prioritisation before a tx is in the mempool (de-prioritising a
         # high-fee transaction so that it's now low fee).