diff --git a/qa/pull-tester/rpc-tests.py b/qa/pull-tester/rpc-tests.py
index d78ffefdd..07ebf587b 100755
--- a/qa/pull-tester/rpc-tests.py
+++ b/qa/pull-tester/rpc-tests.py
@@ -32,13 +32,13 @@ import re
 from tests_config import *
 
 #If imported values are not defined then set to zero (or disabled)
-if not vars().has_key('ENABLE_WALLET'):
+if 'ENABLE_WALLET' not in vars():
     ENABLE_WALLET=0
-if not vars().has_key('ENABLE_BITCOIND'):
+if 'ENABLE_BITCOIND' not in vars():
     ENABLE_BITCOIND=0
-if not vars().has_key('ENABLE_UTILS'):
+if 'ENABLE_UTILS' not in vars():
     ENABLE_UTILS=0
-if not vars().has_key('ENABLE_ZMQ'):
+if 'ENABLE_ZMQ' not in vars():
     ENABLE_ZMQ=0
     
 # python-zmq may not be installed. Handle this gracefully and with some helpful info
diff --git a/qa/rpc-tests/bipdersig-p2p.py b/qa/rpc-tests/bipdersig-p2p.py
index b25872982..cca3aefd1 100755
--- a/qa/rpc-tests/bipdersig-p2p.py
+++ b/qa/rpc-tests/bipdersig-p2p.py
@@ -11,7 +11,7 @@ from test_framework.blocktools import create_coinbase, create_block
 from test_framework.comptool import TestInstance, TestManager
 from test_framework.script import CScript
 from binascii import unhexlify
-import io
+from io import BytesIO
 
 
 '''
@@ -47,7 +47,7 @@ class BIP66Test(ComparisonTestFramework):
         rawtx = node.createrawtransaction(inputs, outputs)
         signresult = node.signrawtransaction(rawtx)
         tx = CTransaction()
-        f = io.BytesIO(unhexlify(signresult['hex']))
+        f = BytesIO(unhexlify(signresult['hex']))
         tx.deserialize(f)
         return tx
 
diff --git a/qa/rpc-tests/fundrawtransaction.py b/qa/rpc-tests/fundrawtransaction.py
index 4445d0ed7..938cb0041 100755
--- a/qa/rpc-tests/fundrawtransaction.py
+++ b/qa/rpc-tests/fundrawtransaction.py
@@ -210,7 +210,7 @@ class RawTransactionsTest(BitcoinTestFramework):
         matchingOuts = 0
         for i, out in enumerate(dec_tx['vout']):
             totalOut += out['value']
-            if out['scriptPubKey']['addresses'][0] in outputs :
+            if out['scriptPubKey']['addresses'][0] in outputs:
                 matchingOuts+=1
             else:
                 assert_equal(i, rawtxfund['changepos'])
diff --git a/qa/rpc-tests/rest.py b/qa/rpc-tests/rest.py
index acc5d943f..f09eda0b9 100755
--- a/qa/rpc-tests/rest.py
+++ b/qa/rpc-tests/rest.py
@@ -14,7 +14,7 @@ from test_framework.util import assert_equal, assert_greater_than, \
 import struct
 import binascii
 import json
-import io
+from io import BytesIO
 from codecs import encode
 from decimal import Decimal
 
@@ -145,7 +145,7 @@ class RESTTest (BitcoinTestFramework):
         binaryRequest += struct.pack("i", 0);
 
         bin_response = http_post_call(url.hostname, url.port, '/rest/getutxos'+self.FORMAT_SEPARATOR+'bin', binaryRequest)
-        output = io.BytesIO()
+        output = BytesIO()
         output.write(bin_response)
         output.seek(0)
         chainHeight = struct.unpack("i", output.read(4))[0]
diff --git a/qa/rpc-tests/smartfees.py b/qa/rpc-tests/smartfees.py
index 8caab8808..3f632696d 100755
--- a/qa/rpc-tests/smartfees.py
+++ b/qa/rpc-tests/smartfees.py
@@ -112,7 +112,7 @@ def check_estimates(node, fees_seen, max_invalid, print_estimates = True):
         print([str(all_estimates[e-1]) for e in [1,2,3,6,15,25]])
     delta = 1.0e-6 # account for rounding error
     last_e = max(fees_seen)
-    for e in filter(lambda x: x >= 0, all_estimates):
+    for e in [x for x in all_estimates if x >= 0]:
         # Estimates should be within the bounds of what transactions fees actually were:
         if float(e)+delta < min(fees_seen) or float(e)-delta > max(fees_seen):
             raise AssertionError("Estimated fee (%f) out of range (%f,%f)"
diff --git a/qa/rpc-tests/test_framework/blockstore.py b/qa/rpc-tests/test_framework/blockstore.py
index 1288521e9..7e8dd2a5a 100644
--- a/qa/rpc-tests/test_framework/blockstore.py
+++ b/qa/rpc-tests/test_framework/blockstore.py
@@ -6,7 +6,7 @@
 from .mininode import CBlock, CBlockHeader, CBlockLocator, CTransaction, msg_block, msg_headers, msg_tx
 
 import sys
-import io
+from io import BytesIO
 import dbm.dumb as dbm
 
 class BlockStore():
@@ -24,7 +24,7 @@ class BlockStore():
             serialized_block = self.blockDB[repr(blockhash)]
         except KeyError:
             return None
-        f = io.BytesIO(serialized_block)
+        f = BytesIO(serialized_block)
         ret = CBlock()
         ret.deserialize(f)
         ret.calc_sha256()
@@ -118,7 +118,7 @@ class TxStore(object):
             serialized_tx = self.txDB[repr(txhash)]
         except KeyError:
             return None
-        f = io.BytesIO(serialized_tx)
+        f = BytesIO(serialized_tx)
         ret = CTransaction()
         ret.deserialize(f)
         ret.calc_sha256()
diff --git a/qa/rpc-tests/test_framework/mininode.py b/qa/rpc-tests/test_framework/mininode.py
index 04a7ef773..36f31e431 100755
--- a/qa/rpc-tests/test_framework/mininode.py
+++ b/qa/rpc-tests/test_framework/mininode.py
@@ -757,9 +757,8 @@ class CTransaction(object):
         self.calc_sha256()
 
     def calc_sha256(self):
-        serialized = self.serialize()
         if self.sha256 is None:
-            self.sha256 = uint256_from_str(hash256(serialized))
+            self.sha256 = uint256_from_str(hash256(self.serialize()))
         self.hash = hash256(self.serialize())[::-1].hex()
 
     def is_valid(self):