How to put an input check for a calculator in python?

print("Welcome to the Kinetic Energy and Gravitational Potential Energy Calculator")
print("Which Calculator would you like to access?")

Choice = str(input("Type in KE for Kinetic Energy and GPE for Gravitational Potential Energy:"))

while Choice != "KE" or "GPE":
    print("Error. You have not entered a valid choice. Please type KE or GPE.")
    Choice = str(input("Type in KE for Kinetic Energy and GPE for Gravitational Potential Energy:"))


while Choice == "KE":
    print("You have chosen the Kinetic Energy Calculator.")
    mass = float(input("Type in the mass of the object in kilograms (kg):"))
    velocity = float(input("Type in the velocity of the object in metres per second (m/s):"))
    result = 0.5*mass*(velocity**2)
    print("The KE is:", result, "J(Joules)")
    Choice = str(input("Type in KE for Kinetic Energy and GPE for Gravitational Potential Energy:"))

while Choice == "GPE":
    print("You have chosen the Gravitational Potential Energy Calculator.")
    mass = float(input("Type in the mass of the object in kilograms (kg):"))
    height = float(input("Type in the height at which the object is in metres (m):"))
    result = 9.81*mass*height
    print("The GPE is:", result, "J(Joules)")
    Choice = str(input("Type in KE for Kinetic Energy and GPE for Gravitational Potential Energy:"))

I have tried using "or" so the check can include both 'KE' and 'GPE', but when you run the program, even if I input KE or GPE, the first while loop keeps going! How can I make it work?

Solution

The problem is in your condition. Since "GPE" is logically True (Non empty string is logically True), the while loop condition is always True, No matter what the choice is.

Change:

Choice != "KE" or "GPE"

to:

Choice != "KE" and Choice != "GPE"

or:

Choice not in ["KE","GPE"]