Practical Programming, 2nd Edition

Repetition Based on User Input

We can use function input in a loop to make the chemical formula translation example from ​Choosing Which Statements to Execute​, interactive. We will ask the user to enter a chemical formula, and our program, which is saved in a file named formulas.py, will print its name. This should continue until the user types quit:

text = ""
while text != "quit":
    text = input("Please enter a chemical formula (or 'quit' to exit): ")
    if text == "quit":
        print("…exiting program")
    elif text == "H2O":
        print("Water")
    elif text == "NH3":
        print("Ammonia")
    elif text == "CH4":
        print("Methane")
    else:
        print("Unknown compound")

Since the loop condition checks the value ...