外部嵌套循环Python的累加器

如果我理解了你想要的(计算该期间降雨量的绝对平均值),这应该可以做到:

number_of_months = 3
years_in_period = int(input("Please enter the number of years in the period. \n"))

total_rain = 0

for year in range(years_in_period):
    yearly_rain = 0
    print('Year', year+1) 
    print('−−−−−−−−−−−−−−−−−')

    for month in range(number_of_months):
        print('Month', month+1, end='')
        monthly_rain = float(input("Please enter rainfall for this month: \n"))

        yearly_rain += monthly_rain

        total_rain += monthly_rain

        average_yearly_rainfall = yearly_rain / number_of_months

    print("Average yearly rainfall of year ", year+1, " is ", average_yearly_rainfall)
    print("Year total rain is", yearly_rain)
    print()


total_months = years_in_period * number_of_months
print("Absolute average of rain/month was", total_rain/total_months)
print("Absolute average of rain/year was", total_rain/years_in_period)