Return a variation of the current dynamic field based on the given
        dynamic part. Use the "format" attribute to create the final name

def get_for(self, dynamic_part):
        """
        Return a variation of the current dynamic field based on the given
        dynamic part. Use the "format" attribute to create the final name
        """
        if not hasattr(self, '_instance'):
            raise ImplementationError('"get_for" can be used only on a bound field')
        name = self.get_name_for(dynamic_part)
        return self._instance.get_field(name)