diff --git a/.arclint b/.arclint
--- a/.arclint
+++ b/.arclint
@@ -135,6 +135,13 @@
         "lint-python-encoding": {
             "type": "lint-python-encoding",
             "include": "(\\.py$)"
+        },
+        "lint-python-shebang": {
+            "type": "lint-python-shebang",
+            "include": "(\\.py$)",
+            "exclude": [
+                "(__init__\\.py$)"
+            ]
         }
     }
 }
diff --git a/arcanist/.phutil_module_cache b/arcanist/.phutil_module_cache
--- a/arcanist/.phutil_module_cache
+++ b/arcanist/.phutil_module_cache
@@ -1 +1 @@
-{"__symbol_cache_version__":11,"ae5b7d3d6b8cf9598ce4abaf0cd56b21":{"have":{"class":{"ExtendedConfigurationDrivenLintEngine":19}},"need":{"function":{"newv":159,"pht":933},"class":{"ArcanistLintEngine":65,"ArcanistConfigurationDrivenLintEngine":171,"PhutilConsole":866},"class\/interface":{"ILintOnce":634}},"xmap":{"ExtendedConfigurationDrivenLintEngine":["ArcanistLintEngine"]}},"2809b09d2021203b43c57da33d1fe8bf":{"have":{"class":{"AssertWithSideEffectsLinter":210}},"need":{"function":{"pht":439},"class":{"ArcanistLinter":246,"ArcanistLintSeverity":926,"Filesystem":1170}},"xmap":{"AssertWithSideEffectsLinter":["ArcanistLinter"]}},"90a8b110dc475955f15bb81d37268cb5":{"have":{"class":{"AutoPEP8FormatLinter":75}},"need":{"function":{"pht":297,"execx":769,"id":1903},"class":{"ArcanistExternalLinter":104,"ArcanistLintMessage":1910,"Filesystem":1754,"ArcanistLinter":2017,"ArcanistLintSeverity":2095}},"xmap":{"AutoPEP8FormatLinter":["ArcanistExternalLinter"]}},"5ea58c19df0397ed8ee0f463d90d6c72":{"have":{"class":{"BoostDependenciesLinter":145}},"need":{"function":{"pht":330,"id":1440},"class":{"GlobalExternalLinter":177,"ArcanistLintMessage":1447,"Filesystem":609,"ArcanistLinter":1524,"ArcanistLintSeverity":1624}},"xmap":{"BoostDependenciesLinter":["GlobalExternalLinter"]}},"38f0c676bff5192a344464142caaa253":{"have":{"class":{"CHeaderLinter":99}},"need":{"function":{"pht":611},"class":{"ArcanistLinter":121,"ArcanistLintSeverity":1060,"Filesystem":1307}},"xmap":{"CHeaderLinter":["ArcanistLinter"]}},"9bb48ec0fe2e9ced8e27d42540d0571c":{"have":{"class":{"CheckDocLinter":106}},"need":{"function":{"pht":321,"id":1845},"class":{"GlobalExternalLinter":129,"ArcanistLintMessage":1852,"Filesystem":729,"ArcanistLinter":1900,"ArcanistLintSeverity":1986}},"xmap":{"CheckDocLinter":["GlobalExternalLinter"]}},"63d19a8745cb2e1200cc26488dc7ad25":{"have":{"class":{"CheckRpcMappingsLinter":131}},"need":{"function":{"pht":310,"id":1386},"class":{"GlobalExternalLinter":162,"ArcanistLintMessage":1393,"Filesystem":573,"ArcanistLinter":1443,"ArcanistLintSeverity":1544}},"xmap":{"CheckRpcMappingsLinter":["GlobalExternalLinter"]}},"6af7410cfea496ff1d4dcc2624b6b8ea":{"have":{"class":{"ClangFormatLinter":79}},"need":{"function":{"pht":302,"execx":781,"id":1653},"class":{"ArcanistExternalLinter":105,"ArcanistLintMessage":1660,"Filesystem":1504,"ArcanistLinter":1767,"ArcanistLintSeverity":1845}},"xmap":{"ClangFormatLinter":["ArcanistExternalLinter"]}},"75579a609dd975aa0226add52700c622":{"have":{"class":{"FileNameLinter":103}},"need":{"function":{"pht":307},"class":{"ArcanistLinter":126,"ArcanistLintSeverity":662,"Filesystem":968}},"xmap":{"FileNameLinter":["ArcanistLinter"]}},"9285ad9415f8ebe564f7119e5a72c559":{"have":{"class":{"FormatStringLinter":146}},"need":{"function":{"pht":377,"csprintf":1492,"id":1872},"class":{"ArcanistExternalLinter":173,"ArcanistLintMessage":1879,"Filesystem":827,"ArcanistLinter":1956,"ArcanistLintSeverity":2044}},"xmap":{"FormatStringLinter":["ArcanistExternalLinter"]}},"2e11dd9ad67e594f863bc46ac59ea37e":{"have":{"class":{"GlobalExternalLinter":199}},"need":{"class":{"ArcanistExternalLinter":228},"interface":{"ILintOnce":262}},"xmap":{"GlobalExternalLinter":["ArcanistExternalLinter","ILintOnce"]}},"b2403124ec3e8be6cb4d10bf0f6c4134":{"have":{"interface":{"ILintOnce":69}},"need":[],"xmap":[]},"1f9bac7956f4f948a187828dcc6ba2d0":{"have":{"class":{"IncludeGuardLinter":98}},"need":{"function":{"pht":368},"class":{"ArcanistLinter":125,"ArcanistLintSeverity":721,"Filesystem":970}},"xmap":{"IncludeGuardLinter":["ArcanistLinter"]}},"2cbb6e7228d81557f777ad648704f343":{"have":{"class":{"IncludeQuotesLinter":100}},"need":{"function":{"pht":306},"class":{"ArcanistLinter":128,"ArcanistLintSeverity":663,"Filesystem":964}},"xmap":{"IncludeQuotesLinter":["ArcanistLinter"]}},"f151089cf79fdb8257b2272ed4782d88":{"have":{"class":{"IncludeSourceLinter":99}},"need":{"function":{"pht":391},"class":{"ArcanistLinter":127,"ArcanistLintSeverity":699,"Filesystem":938}},"xmap":{"IncludeSourceLinter":["ArcanistLinter"]}},"ce5dee893bedb5d93466655eede8ac47":{"have":{"class":{"LocaleDependenceLinter":160}},"need":{"function":{"pht":5429},"class":{"ArcanistLinter":191,"ArcanistLintSeverity":5932,"Filesystem":6178}},"xmap":{"LocaleDependenceLinter":["ArcanistLinter"]}},"6f2f22dd0f259fb2eaa284b4fab3bc29":{"have":{"class":{"PythonFormatLinter":123}},"need":{"function":{"pht":353,"id":1838},"class":{"ArcanistExternalLinter":150,"ArcanistLintMessage":1845,"Filesystem":776,"ArcanistLinter":1970,"ArcanistLintSeverity":2053}},"xmap":{"PythonFormatLinter":["ArcanistExternalLinter"]}},"09a933fbbf135320585be52750d93831":{"have":{"class":{"StdintLinter":90}},"need":{"function":{"pht":280},"class":{"ArcanistLinter":111,"ArcanistLintSeverity":589,"Filesystem":897}},"xmap":{"StdintLinter":["ArcanistLinter"]}},"25781df78f6eebfb223296b8265e9d19":{"have":{"class":{"TestsLinter":103}},"need":{"function":{"pht":318,"id":2629},"class":{"ArcanistExternalLinter":123,"ArcanistLi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\ No newline at end of file
+{"__symbol_cache_version__":11,"ae5b7d3d6b8cf9598ce4abaf0cd56b21":{"have":{"class":{"ExtendedConfigurationDrivenLintEngine":19}},"need":{"function":{"newv":159,"pht":933},"class":{"ArcanistLintEngine":65,"ArcanistConfigurationDrivenLintEngine":171,"PhutilConsole":866},"class\/interface":{"ILintOnce":634}},"xmap":{"ExtendedConfigurationDrivenLintEngine":["ArcanistLintEngine"]}},"2809b09d2021203b43c57da33d1fe8bf":{"have":{"class":{"AssertWithSideEffectsLinter":210}},"need":{"function":{"pht":439},"class":{"ArcanistLinter":246,"ArcanistLintSeverity":926,"Filesystem":1170}},"xmap":{"AssertWithSideEffectsLinter":["ArcanistLinter"]}},"90a8b110dc475955f15bb81d37268cb5":{"have":{"class":{"AutoPEP8FormatLinter":75}},"need":{"function":{"pht":297,"execx":769,"id":1903},"class":{"ArcanistExternalLinter":104,"ArcanistLintMessage":1910,"Filesystem":1754,"ArcanistLinter":2017,"ArcanistLintSeverity":2095}},"xmap":{"AutoPEP8FormatLinter":["ArcanistExternalLinter"]}},"5ea58c19df0397ed8ee0f463d90d6c72":{"have":{"class":{"BoostDependenciesLinter":145}},"need":{"function":{"pht":330,"id":1440},"class":{"GlobalExternalLinter":177,"ArcanistLintMessage":1447,"Filesystem":609,"ArcanistLinter":1524,"ArcanistLintSeverity":1624}},"xmap":{"BoostDependenciesLinter":["GlobalExternalLinter"]}},"38f0c676bff5192a344464142caaa253":{"have":{"class":{"CHeaderLinter":99}},"need":{"function":{"pht":611},"class":{"ArcanistLinter":121,"ArcanistLintSeverity":1060,"Filesystem":1307}},"xmap":{"CHeaderLinter":["ArcanistLinter"]}},"9bb48ec0fe2e9ced8e27d42540d0571c":{"have":{"class":{"CheckDocLinter":106}},"need":{"function":{"pht":321,"id":1845},"class":{"GlobalExternalLinter":129,"ArcanistLintMessage":1852,"Filesystem":729,"ArcanistLinter":1900,"ArcanistLintSeverity":1986}},"xmap":{"CheckDocLinter":["GlobalExternalLinter"]}},"63d19a8745cb2e1200cc26488dc7ad25":{"have":{"class":{"CheckRpcMappingsLinter":131}},"need":{"function":{"pht":310,"id":1386},"class":{"GlobalExternalLinter":162,"ArcanistLintMessage":1393,"Filesystem":573,"ArcanistLinter":1443,"ArcanistLintSeverity":1544}},"xmap":{"CheckRpcMappingsLinter":["GlobalExternalLinter"]}},"75579a609dd975aa0226add52700c622":{"have":{"class":{"FileNameLinter":103}},"need":{"function":{"pht":307},"class":{"ArcanistLinter":126,"ArcanistLintSeverity":662,"Filesystem":968}},"xmap":{"FileNameLinter":["ArcanistLinter"]}},"9285ad9415f8ebe564f7119e5a72c559":{"have":{"class":{"FormatStringLinter":146}},"need":{"function":{"pht":377,"csprintf":1492,"id":1872},"class":{"ArcanistExternalLinter":173,"ArcanistLintMessage":1879,"Filesystem":827,"ArcanistLinter":1956,"ArcanistLintSeverity":2044}},"xmap":{"FormatStringLinter":["ArcanistExternalLinter"]}},"2e11dd9ad67e594f863bc46ac59ea37e":{"have":{"class":{"GlobalExternalLinter":199}},"need":{"class":{"ArcanistExternalLinter":228},"interface":{"ILintOnce":262}},"xmap":{"GlobalExternalLinter":["ArcanistExternalLinter","ILintOnce"]}},"b2403124ec3e8be6cb4d10bf0f6c4134":{"have":{"interface":{"ILintOnce":69}},"need":[],"xmap":[]},"1f9bac7956f4f948a187828dcc6ba2d0":{"have":{"class":{"IncludeGuardLinter":98}},"need":{"function":{"pht":368},"class":{"ArcanistLinter":125,"ArcanistLintSeverity":721,"Filesystem":970}},"xmap":{"IncludeGuardLinter":["ArcanistLinter"]}},"2cbb6e7228d81557f777ad648704f343":{"have":{"class":{"IncludeQuotesLinter":100}},"need":{"function":{"pht":306},"class":{"ArcanistLinter":128,"ArcanistLintSeverity":663,"Filesystem":964}},"xmap":{"IncludeQuotesLinter":["ArcanistLinter"]}},"f151089cf79fdb8257b2272ed4782d88":{"have":{"class":{"IncludeSourceLinter":99}},"need":{"function":{"pht":391},"class":{"ArcanistLinter":127,"ArcanistLintSeverity":699,"Filesystem":938}},"xmap":{"IncludeSourceLinter":["ArcanistLinter"]}},"ce5dee893bedb5d93466655eede8ac47":{"have":{"class":{"LocaleDependenceLinter":160}},"need":{"function":{"pht":5429},"class":{"ArcanistLinter":191,"ArcanistLintSeverity":5932,"Filesystem":6178}},"xmap":{"LocaleDependenceLinter":["ArcanistLinter"]}},"6f2f22dd0f259fb2eaa284b4fab3bc29":{"have":{"class":{"PythonFormatLinter":123}},"need":{"function":{"pht":353,"id":1838},"class":{"ArcanistExternalLinter":150,"ArcanistLintMessage":1845,"Filesystem":776,"ArcanistLinter":1970,"ArcanistLintSeverity":2053}},"xmap":{"PythonFormatLinter":["ArcanistExternalLinter"]}},"03cf226fe177a9fce7dc046816cc466b":{"have":{"class":{"PythonOpenFileEncodingLinter":111}},"need":{"function":{"pht":325},"class":{"ArcanistLinter":148,"ArcanistLintSeverity":687,"Filesystem":991}},"xmap":{"PythonOpenFileEncodingLinter":["ArcanistLinter"]}},"09a933fbbf135320585be52750d93831":{"have":{"class":{"StdintLinter":90}},"need":{"function":{"pht":280},"class":{"ArcanistLinter":111,"ArcanistLintSeverity":589,"Filesystem":897}},"xmap":{"StdintLinter":["ArcanistLinter"]}},"25781df78f6eebfb223296b8265e9d19":{"have":{"class":{"TestsLinter":103}},"need":{"function":{"pht":318,"id":2629},"class":{"ArcanistExternalLinter":123,"ArcanistLintMessage":2636,"Filesystem":776,"ArcanistLinter":2684,"ArcanistLi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\ No newline at end of file
diff --git a/arcanist/__phutil_library_map__.php b/arcanist/__phutil_library_map__.php
--- a/arcanist/__phutil_library_map__.php
+++ b/arcanist/__phutil_library_map__.php
@@ -27,6 +27,7 @@
     'LocaleDependenceLinter' => 'linter/LocaleDependenceLinter.php',
     'PythonFormatLinter' => 'linter/PythonFormatLinter.php',
     'PythonOpenFileEncodingLinter' => 'linter/PythonOpenFileEncodingLinter.php',
+    'PythonShebangLinter' => 'linter/PythonShebangLinter.php',
     'StdintLinter' => 'linter/StdintLinter.php',
     'TestsLinter' => 'linter/TestsLinter.php',
   ),
@@ -52,6 +53,7 @@
     'LocaleDependenceLinter' => 'ArcanistLinter',
     'PythonFormatLinter' => 'ArcanistExternalLinter',
     'PythonOpenFileEncodingLinter' => 'ArcanistLinter',
+    'PythonShebangLinter' => 'ArcanistLinter',
     'StdintLinter' => 'ArcanistLinter',
     'TestsLinter' => 'ArcanistExternalLinter',
   ),
diff --git a/arcanist/linter/PythonShebangLinter.php b/arcanist/linter/PythonShebangLinter.php
new file mode 100644
--- /dev/null
+++ b/arcanist/linter/PythonShebangLinter.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * Enforce python scripts shebang to #/usr/bin/env python3.
+ */
+final class PythonShebangLinter extends ArcanistLinter {
+
+  const BAD_SHEBANG_FOUND = 1;
+
+  public function getInfoName() {
+    return 'lint-python-shebang';
+  }
+
+  public function getInfoDescription() {
+    return pht('Enforce the declaration of python 3 environment in shebangs.');
+  }
+
+  public function getLinterName() {
+    return 'PYTHON_SHEBANG';
+  }
+
+  public function getLinterConfigurationName() {
+    return 'lint-python-shebang';
+  }
+
+  public function getLintSeverityMap() {
+    return array(
+      self::BAD_SHEBANG_FOUND => ArcanistLintSeverity::SEVERITY_ERROR,
+    );
+  }
+
+  public function getLintNameMap() {
+    return array(
+      self::BAD_SHEBANG_FOUND => pht('Missing or unexpected shebang.'),
+    );
+  }
+
+  public function lintPath($path) {
+    $absPath = Filesystem::resolvePath($path, $this->getProjectRoot());
+    $fileContent = Filesystem::readFile($absPath);
+
+    if (!preg_match_all("%^#!/usr/bin/env python3%", $fileContent)) {
+      return $this->raiseLintAtPath(
+        self::BAD_SHEBANG_FOUND,
+        pht("Shebang should be #!/usr/bin/env python3"));
+    }
+  }
+}
diff --git a/contrib/devtools/test-security-check.py b/contrib/devtools/test-security-check.py
--- a/contrib/devtools/test-security-check.py
+++ b/contrib/devtools/test-security-check.py
@@ -1,11 +1,10 @@
-#!/usr/bin/env python2
-# Copyright (c) 2015-2016 The Bitcoin Core developers
+#!/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
 
@@ -24,8 +23,8 @@
 
 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())
 
diff --git a/contrib/testgen/base58.py b/contrib/testgen/base58.py
--- a/contrib/testgen/base58.py
+++ b/contrib/testgen/base58.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # Copyright (c) 2012-2017 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
diff --git a/src/bench/data/convert-raw-to-header.py b/src/bench/data/convert-raw-to-header.py
--- a/src/bench/data/convert-raw-to-header.py
+++ b/src/bench/data/convert-raw-to-header.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) 2019 The Bitcoin developers
 
 import sys
diff --git a/src/test/data/generate_header.py b/src/test/data/generate_header.py
--- a/src/test/data/generate_header.py
+++ b/src/test/data/generate_header.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) 2018 The Bitcoin developers
 
 import sys
diff --git a/test/functional/test_framework/authproxy.py b/test/functional/test_framework/authproxy.py
--- a/test/functional/test_framework/authproxy.py
+++ b/test/functional/test_framework/authproxy.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # Copyright (c) 2011 Jeff Garzik
 #
 # Previous copyright, from python-jsonrpc/jsonrpc/proxy.py:
diff --git a/test/functional/test_framework/key.py b/test/functional/test_framework/key.py
--- a/test/functional/test_framework/key.py
+++ b/test/functional/test_framework/key.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # Copyright (c) 2011 Sam Rushing
 """ECC secp256k1 OpenSSL wrapper.
 
diff --git a/test/functional/test_framework/txtools.py b/test/functional/test_framework/txtools.py
--- a/test/functional/test_framework/txtools.py
+++ b/test/functional/test_framework/txtools.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 import random
 
 from .cdefs import MAX_TXOUT_PUBKEY_SCRIPT, MIN_TX_SIZE