def calc_seeds_cost(crop, ya, harvest_weight):
    """
        Seeds Calculator
        Notes
        ------
            :param crop: The crop that is selected to be grown on the farm
            :param ya: The expected yield for that crop
            :param harvest_weight: The harvest weight selected for that crop
            The seeds required are 40% more than the plants harvested. This is to account for error, unsuccessful
            propagation or thinning.
            :return: The cost per seed, and the number of seeds required to calculate the overall seed cost per year
    """
    if crop == 'lettuce':
        cost_per_seed = 0.10
    else:
        raise RuntimeError("Unknown crop: {}".format(crop))
    seeds_required = (ya/harvest_weight)*1.4
    seeds_cost = seeds_required * cost_per_seed  # costs of seeds
    return seeds_cost