How to stop a traceback call after making a deliberate mistake?

Question

I am making a calculator which executes only a certain number of operations, if anything else is entered it prints a reminder message. But during that process an name error occurs, just after it prints'a'. where am i going wrong?

if Operation == '+':
    c = a + b

elif Operation == '-':
    c = a - b

elif Operation == '*':
    c = a * b

elif Operation == '/':
    c = a / b
else:
    print('Read the Instructions again, dimmwit')


print('Your answer is', c)

print('Thanks! Have a great time!')

And pls give a few suggestions on how should i improve my code.

Answer 1

Because of this:

else:
    print('Read the Instructions again, dimmwit')

It is possible that by the time

print('Your answer is', c)

is reached, there is no c defined if that else route is taken.

If you make this a function, such as:

def print_result(operation, a, b):
    if operation == '+':
        c = a + b

    elif operation == '-':
        c = a - b

    elif operation == '*':
        c = a * b

    elif operation == '/':
        c = a / b

    else:
        print('Read the Instructions again, dimmwit')
        return

    print('Your answer is', c)
    print('Thanks! Have a great time!')

Then you can stop early with the return , instead of attempting to print an answer c that is never computed.

Answer 2

You really should also post the particular NameError you're getting, and the traceback. (And your full code.)

Anyway, the problem is you're not initializing c to anything, so when control falls out of the "insult the user" else , trying to print c can't happen.

Give c some value in all cases, then check whether you actually did an operation:

c = None
if Operation == "+":
    c = a + b
elif Operation == "-":
    c = a - b
elif Operation == "*":
    c = a * b
elif Operation == "/":
    c = a / b
else:
    print("Read the Instructions again, dimmwit")

if c is not None:
    print("Your answer is", c)
    print("Thanks! Have a great time!")

Better still, do the computation in a function of its own, and output things to the user elsewhere:

def compute(operation, a, b):
    if operation == "+":
        return a + b
    elif operation == "-":
        return a - b
    elif operation == "*":
        return a * b
    elif operation == "/":
        return a / b
    return None


c = compute(operation, a, b)

if c is not None:
    print("Your answer is", c)
    print("Thanks! Have a great time!")
else:
    print("Please read the instructions again.")