AutoSlugFied: Allow function for populate_from.

shared/utils/models/slugs.py

@@ -52,6 +52,9 @@ class AutoSlugField(django_fields.SlugField):
         value = getattr(model_instance, self.attname)
         if not value:
             if hasattr(self, 'populate_from'):
+                if callable(self.populate_from):
+                    value = self.populate_from(model_instance, self)
+                else:
                     # Follow dotted path (e.g. "occupation.corporation.name")
                     value = reduce(lambda obj, attr: getattr(obj, attr),
                         self.populate_from.split("."), model_instance)