def format_one_rate(rate, from_amt, from_curr, to_curr):

    return "{:g} {} = {:g} {}".format(

        from_amt, from_curr, rate.convert(from_amt, from_curr, to_curr), to_curr)

def format_rate_pair(rate, from_curr, to_curr):

    yield format_one_rate(rate, 1, from_curr, to_curr)

    yield format_one_rate(rate, 1, to_curr, from_curr)

def run(config, stdout, stderr):

    loaders = config.get_loaders()

    with loaders.historical(config.args.date, config.args.base) as rate_json:

    if not config.args.from_currency:

        for from_curr in sorted(rate.rates):

            print(*format_rate_pair(rate, from_curr, config.args.to_currency),

                  sep='\n', file=stdout)

    elif config.args.amount is None:

        print(*format_rate_pair(rate, config.args.from_currency, config.args.to_currency),