Python isdigit if statement

You can use a while loop and check for a valid input.

Try this code:

def main():
    month_names = ['January', 'February', 'March', 'April', 'May', 'June', 'July',
                   'August', 'September', 'October', 'November', 'December']
    total_rain = [0] * 12 # to store the total rain per month
    sum = 0

    for i in range(12):
        rain = None
        while not rain:  # while invalid input
            rain = input("Enter the total rain in " + month_names[i] + ": ")
            if not rain.isnumeric():  # not number
                print("Invalid!")
                rain = None  # retry input
        total_rain[i] = int(rain)
        sum += total_rain[i] #adding rain to sum
         #printing result
    s = "\n\nTotal Rainfall: " + str(sum) + "\nAverage monthly rainfall: " + str(sum/12) + "\nLowest Rainfall: " + str(min (total_rain))
          + " In month of " +str(month_names[total_rain.index(min(total_rain))])+"\nHighest Rainfall: " + str(max(total_rain))+" In month of " +
          str(month_names[total_rain.index(max(total_rain))])
    print(s)
    return s

main()

Output

Enter the total rain in January: asdfad
Invalid!
Enter the total rain in January: 
Invalid!
Enter the total rain in January: 12
Enter the total rain in February: 23
Enter the total rain in March: afad
Invalid!
Enter the total rain in March: 45
Enter the total rain in April: afcasdc
Invalid!
Enter the total rain in April: sc
Invalid!

Output 2

Enter the total rain in January: 1
Enter the total rain in February: 2
Enter the total rain in March: 3
Enter the total rain in April: 4
Enter the total rain in May: 5
Enter the total rain in June: 6
Enter the total rain in July: 7
Enter the total rain in August: 8
Enter the total rain in September: 9
Enter the total rain in October: 10
Enter the total rain in November: 11
Enter the total rain in December: 12


Total Rainfall: 78
Average monthly rainfall: 6.5
Lowest Rainfall: 1 In month of January
Highest Rainfall: 12 In month of December