Update io modules for py3, ISSUE with create_transaction function

qa/rpc-tests/tx_expiry_helper.py

@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # Copyright (c) 2019 The Zcash developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or https://www.opensource.org/licenses/mit-license.php .
@@ -7,9 +8,9 @@
 #
 from test_framework.mininode import CTransaction, NodeConnCB, mininode_lock, msg_ping, \
     msg_pong
-from test_framework.util import fail
+from test_framework.util import fail, hex_str_to_bytes, bytes_to_hex_str
 
-import cStringIO
+import io
 import time
 
 from binascii import hexlify, unhexlify
@@ -86,13 +87,13 @@ def create_transaction(node, coinbase, to_address, amount, expiry_height):
     tx = CTransaction()
 
     # Set the expiry height
-    f = cStringIO.StringIO(unhexlify(rawtx))
+    f = io.BytesIO(unhexlify(rawtx))
     tx.deserialize(f)
     tx.nExpiryHeight = expiry_height
     rawtx = hexlify(tx.serialize())
 
     signresult = node.signrawtransaction(rawtx)
-    f = cStringIO.StringIO(unhexlify(signresult['hex']))
+    f = io.BytesIO(unhexlify(signresult['hex']))
     tx.deserialize(f)
     tx.rehash()
     return tx