Merge #12972: Add python3 script shebang lint

2bff472992 [contrib] convert test-security-check to python3 (John Newbery)
958bf40489 add lint tool to check python3 shebang (practicalswift)

Pull request description:

  base58.py can executed by python3

Tree-SHA512: 30511204feefd4ccd5b4bf698fb88e516633e692dc95d31fe957b1c0c4879de25906355b28a5a0522171887315c8464a611e601ff00540db172d5bd463ee13d9

contrib/devtools/lint-python-shebang.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+# Shebang must use python3 (not python or python2)
+EXIT_CODE=0
+for PYTHON_FILE in $(git ls-files -- "*.py"); do
+    if [[ $(head -c 2 "${PYTHON_FILE}") == "#!" &&
+          $(head -n 1 "${PYTHON_FILE}") != "#!/usr/bin/env python3" ]]; then
+        echo "Missing shebang \"#!/usr/bin/env python3\" in ${PYTHON_FILE} (do not use python or python2)"
+        EXIT_CODE=1
+    fi
+done
+exit ${EXIT_CODE}

contrib/devtools/test-security-check.py

@@ -1,11 +1,10 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright (c) 2015-2017 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 '''
 Test script for security-check.py
 '''
-from __future__ import division,print_function
 import subprocess
 import unittest
 
@@ -22,7 +21,7 @@ def write_testcode(filename):
 
 def call_security_check(cc, source, executable, options):
     subprocess.check_call([cc,source,'-o',executable] + options)
-    p = subprocess.Popen(['./security-check.py',executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
+    p = subprocess.Popen(['./security-check.py',executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE, universal_newlines=True)
     (stdout, stderr) = p.communicate()
     return (p.returncode, stdout.rstrip())