def on_cleanup_error(function, path, excinfo):
                click.secho("warning: failed to remove file or directory: {}\n"
                            "please delete it manually.".format(path),
                            fg="red")
def deadline_for_course(cls, course_key):
        """
        Retrieve the verification deadline for a particular course.

        Arguments:
            course_key (CourseKey): The identifier for the course.

        Returns:
            datetime or None

        """
        try:
            deadline = cls.objects.get(course_key=course_key)
            return deadline.deadline
        except cls.DoesNotExist:
            return None