'Returns the group from the specified user position to which the user is assigned.
If the user has not yet been assigned, a group will be randomly chosen for them if assign flag is True.'

@classmethod
def get_group_for_user(cls, course_key, user, user_partition, assign=True):

    partition_key = cls.key_for_partition(user_partition)
    group_id = course_tag_api.get_course_tag(user, course_key, partition_key)
    group = None
    if (group_id is not None):
        try:
            group = user_partition.get_group(int(group_id))
        except NoSuchUserPartitionGroupError:
            log.warn('group    not    found    in    RandomUserPartitionScheme:    %r', {'requested_partition_id': user_partition.id, 'requested_group_id': group_id}, exc_info=True)
    if ((group is None) and assign and (not course_tag_api.BulkCourseTags.is_prefetched(course_key))):
        if (not user_partition.groups):
            raise UserPartitionError('Cannot    assign    user    to    an    empty    user    partition')
        group = cls.RANDOM.choice(user_partition.groups)
        course_tag_api.set_course_tag(user, course_key, partition_key, group.id)
        event_name = 'xmodule.partitions.assigned_user_to_partition'
        event_info = {'group_id': group.id, 'group_name': group.name, 'partition_id': user_partition.id, 'partition_name': user_partition.name}
        with tracker.get_tracker().context(event_name, {}):
            tracker.emit(event_name, event_info)
    return group
