Problem with operation in a simple code to convert your weight in weight of another planet

I decided to write the same program I did in C++ in Python. The only problem is it doesn’t work. I tried tweaking here and there but my result is always the same: "your weight is none kg"

g = 9.81

def operation(x,y):
    (x/g)*y

kg = float(input("Please enter your weight in Kg on earth: "))
print("1)mercury")
print("2)venus")
print("3)mars")
print("4)jupiter")
print("5)saturn")
print("6)uranus")
print("7)neptune")
print("8)pluto")

while True:
    planet = input("Please in what planet do you want to see your weight? ")
    if planet in("1","2","3","4","5","6","7","8"):
        if planet == "1":
            print("your weight in mercury is: ",operation(kg,3.61), "kg")
        elif planet == "2":
            print("your weight in venus is: ",operation(kg,8.87),"kg")
        elif planet == "3":
            print("your weight in mars is: ",operation(kg,3.721),"kg")
        elif planet == "4":
            print("your weight in jupiter",operation(kg,26),"kg")
        elif planet == "5":
            print("your weight in saturn is: ",operation(kg,11.2),"kg")
        elif planet == "6":
            print("your weight in uranus is: ", operation(kg,10.5),"kg")
        elif planet == "7":
            print("your weight in neptune is: ",operation(kg,13.3),"kg")
        elif planet == "8":
            print("your weight on pluto is: ",operation(kg,0.61),"kg")
        continue_1 = input("Do you wish to know your weight on another planet? (yes/no)")
        if continue_1 == "no":
            break
    else:
        print("Thank you for using our program")

>Solution :

I see you are missing return in the operation function.

def operation(x,y):
    return (x/g)*y