Get the value of the field

def get(self, instance, **kw):
        """Get the value of the field
        """
        # Gracefully avoid programming errors in Computed fields
        try:
            return self._get(instance, **kw)
        except AttributeError:
            logger.error("Could not get the value of the computed field '{}'"
                         .format(self.get_field_name()))
            return None