Make doubly sure that we fail quickly on future Python 3.x versions. …

…refs #1775

Signed-off-by: David-Sarah Hopwood <david-sarah@jacaranda.org>

bin/tahoe-script.template

@@ -1,7 +1,7 @@
 #!/bin/false # You must specify a python interpreter.
-ur"Tahoe-LAFS does not run under Python 3. Please use a version of Python between 2.5 and 2.7.x inclusive."
+import sys; assert sys.version_info < (3,), ur"Tahoe-LAFS does not run under Python 3. Please use a version of Python between 2.5 and 2.7.x inclusive."
 
-import sys, os, subprocess
+import os, subprocess
 
 where = os.path.realpath(sys.argv[0])
 base = os.path.dirname(os.path.dirname(where))
@@ -63,7 +63,7 @@ if sys.platform == "win32":
     # Note that this doesn't escape \x7F. If it did, test_unicode_arguments_and_output
     # in test_runner.py wouldn't work.
     def mangle(s):
-        return str(re.sub(ur'[^\x20-\x7F]', lambda m: u'\x7F%x;' % (ord(m.group(0)),), s))
+        return str(re.sub(u'[^\\x20-\\x7F]', lambda m: u'\x7F%x;' % (ord(m.group(0)),), s))
 
     argv = [mangle(argv_unicode[i]) for i in xrange(0, argc.value)]
 

setup.py

@@ -1,6 +1,6 @@
 #! /usr/bin/env python
 # -*- coding: utf-8 -*-
-ur"Tahoe-LAFS does not run under Python 3. Please use a version of Python between 2.5 and 2.7.x inclusive."
+import sys; assert sys.version_info < (3,), ur"Tahoe-LAFS does not run under Python 3. Please use a version of Python between 2.5 and 2.7.x inclusive."
 
 # Tahoe-LAFS -- secure, distributed storage grid
 #
@@ -10,7 +10,7 @@
 #
 # See the docs/about.rst file for licensing information.
 
-import glob, os, stat, subprocess, sys, re
+import glob, os, stat, subprocess, re
 
 ##### sys.path management