Merge pull request #90 from dhui/pythonic

Use getattr() instead of hasattr() since it does one less lookup.

jsonfield/fields.py

@@ -72,7 +72,7 @@ def pre_init(self, value, obj):
             # Make sure the primary key actually exists on the object before
             # checking if it's empty. This is a special case for South datamigrations
             # see: https://github.com/bradjasper/django-jsonfield/issues/52
-            if hasattr(obj, "pk") and obj.pk is not None:
+            if getattr(obj, "pk", None) is not None:
                 if isinstance(value, six.string_types):
                     try:
                         return json.loads(value, **self.load_kwargs)