Returns a `Counter` object that counts the number of task with
        given status (use the string representation of the status as key).

def status_counter(self):
        """
        Returns a `Counter` object that counts the number of task with
        given status (use the string representation of the status as key).
        """
        counter = collections.Counter()

        for task in self:
            counter[str(task.status)] += 1

        return counter