def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def set_deadline(cls, course_key, deadline, is_explicit=False):
        """
        Configure the verification deadline for a course.

        If `deadline` is `None`, then the course will have no verification
        deadline.  In this case, users will be able to verify for the course
        at any time.

        Arguments:
            course_key (CourseKey): Identifier for the course.
            deadline (datetime or None): The verification deadline.

        """
        if deadline is None:
            VerificationDeadline.objects.filter(course_key=course_key).delete()
        else:
            record, created = VerificationDeadline.objects.get_or_create(
                course_key=course_key,
                defaults={"deadline": deadline, "deadline_is_explicit": is_explicit}
            )

            if not created:
                record.deadline = deadline
                record.deadline_is_explicit = is_explicit
                record.save()