Use media str method for admin

media/models.py

@@ -63,8 +63,10 @@ class Media(models.Model):
     )
 
     def __str__(self):
-        return str(self.title) + ' - ' + str(self.subtitle) \
-               + ' - ' + str(self.authors.all().first())
+        if self.subtitle:
+            return "{} : {}".format(self.title, self.subtitle)
+        else:
+            return self.title
 
     class Meta:
         verbose_name = _("medium")