fix compatibility issues with python 2.6, and disable testing on django versions 1.6.x and 1.7.x on python 3.5

.travis.yml

@@ -36,6 +36,10 @@ matrix:
       env: DJANGO=Django==1.8.5
     - python: "2.6"
       env: DJANGO=Django==1.9b1
+    - python: "3.5"
+      env: DJANGO=Django==1.6.11
+    - python: "3.5"
+      env: DJANGO=Django==1.7.10
 
 after_success:
   - coveralls --verbose

defender/tests.py

@@ -615,7 +615,7 @@ class AccessAttemptTest(DefenderTestCase):
         # same IP different, usernames
         ip = '74.125.239.60'
         for i in range(0, config.FAILURE_LIMIT+10):
-            login_username = u"{}{}".format(username, i)
+            login_username = u"{0}{1}".format(username, i)
             response = self._login(username=login_username, remote_addr=ip)
             # Check if we are in the same login page
             self.assertContains(response, LOGIN_FORM_KEY)