Deletes scheduled jobs marked with the given tag, or all jobs
        if tag is omitted.

        :param tag: An identifier used to identify a subset of
                    jobs to delete

def clear(self, tag=None):
        """
        Deletes scheduled jobs marked with the given tag, or all jobs
        if tag is omitted.

        :param tag: An identifier used to identify a subset of
                    jobs to delete
        """
        if tag is None:
            del self.jobs[:]
        else:
            self.jobs[:] = (job for job in self.jobs if tag not in job.tags)