def set(self, dict_name, key, value, priority=None):
        '''Set a single value for a single key.

        This requires a session lock.

        :param str dict_name: name of the dictionary to update
        :param str key: key to update
        :param str value: value to assign to `key`
        :param int priority: priority score for the value (if any)

        '''
        if priority is not None:
            priorities = {key: priority}
        else:
            priorities = None
        self.update(dict_name, {key: value}, priorities=priorities)
Set a single value for a single key.

        This requires a session lock.

        :param str dict_name: name of the dictionary to update
        :param str key: key to update
        :param str value: value to assign to `key`
        :param int priority: priority score for the value (if any)