def METHOD_NAME(self, index, fan_index):
    """
    Retrieves the speed of fan, in rpm, denoted by 1-based <fan_index> of a power 
            supply unit (PSU) defined by 1-based index <index>
    :param index: An integer, 1-based index of the PSU of which to query fan speed
    :param fan_index: An integer, 1-based index of the PSU-fan of which to query speed
    :return: An integer, value of PSU-fan speed in rpm if PSU-fan is good, else zero
    """
    if index is None:
        raise RuntimeError("index shouldn't be None")
    if fan_index > self.MAX_PSU_FAN:
        raise RuntimeError("fan_index ({}) shouldn't be greater than {}".format(fan_index, self.MAX_PSU_FAN))
    if not self.get_psu_presence(index) or not self.get_psu_status(index):
        return 0
    fan_speed = self._read_file(self.fan_speed, index)
    return fan_speed