fix python 3 incompatibility

7 jobs for master in 34 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #51342
py27-django110

00:00:17

passed #51343
py27-django111

00:00:18

passed #51341
py27-django18

00:00:18

passed #51345
py36-django110

00:00:18

passed #51346
py36-django111

00:00:15

passed #51344
py36-django18

00:00:19

passed #51347
py36-django20

00:00:15