Cannot figure out what is wrong

[wavic]

The calculation function doesn't return anything.
You can add the planet as a parameter and create a dict.

lbs = ask_weight()
def calculation(lbs, planet):
    mass = lbs/9.807
    weight = {
        'mercury': mass*3.7,
        'venus':mass*8.87,
        'mars': mass*3.71,
        'jupiter': mass*24.92,
        'saturn': mass*10.44,
        'uranus': mass*8.87,
        'neptune': mass*11.15,
        'pluto': mass*0.58} # pluto. Actually Pluto is no more a part of the nine. http://www.bbc.com/news/science-environment-33462184

     return weight[planet]

def ask_weight():
    lbs = float(input("How many pounds do you weigh? "))
    return lbs # the function have to return a value. lbs is a local to the fuction variable.

def ask_planet():
    planet = input("Which planet would you like to know your weight for? ")
    return planet # same here

And then:
 

    planet = ask_planet().lower()
    lbs = ask_weight()

    # if is not needed because we have a dict and we using the planet name to determine the desired value
    print("Your weight on {} would be {} pounds.".format(planet.title(), calculation(lbs, planet))