specific string input exception handling

I wrote this function to get user input of an integer and two strings (letters C F or K) for a temperature conversion exercise. I want to control the specificity of the input, i.e. that only the correct letters are entered and not another using the exception handling try: except: statements. The inputs are passed to the print function regardless, so even if you input say a “D”. I tried many things, but I am totally drawing a blank. Please help, need try: except to help me understand this in Python. Thanks. The code:

def gettemp ():
    while True:
        tempin = input ("Enter temperature value:")
        scalein = input ("Enter temperature scale (C/F/K):")
        scaleout = input ("Enter scale to convert to (C/F/K):")
        try:
            tempin == int (tempin)
            scalein == "C" or "F" or "K"
            scaleout == "C" or "F" or "K"
            return tempin, scalein, scaleout
        except NameError:
            print ("Please reenter:")
        
print (gettemp())

>Solution :

Your approach using or is wrong. Using or on strings will return the first non-falsey string, in your case scalein and scaleout will both become "C". Check if the scales are valid and raise an exception if they’re not:

def gettemp():
    while True:
        tempin = input("Enter temperature value:")
        scalein = input("Enter temperature scale (C/F/K):")
        scaleout = input("Enter scale to convert to (C/F/K):")
        try:
            tempin = int(tempin)  # also make sure to use the right equals
            valid = ("C", "F", "K")
            if scalein not in valid or scaleout not in valid:
                raise ValueError
            return tempin, scalein, scaleout
        except ValueError:
            print("Please reenter:")
        
print(gettemp())

You can also achieve this behavior without using a try-except block:

def gettemp():
    while True:
        tempin = input("Enter temperature value:")
        scalein = input("Enter temperature scale (C/F/K):")
        scaleout = input("Enter scale to convert to (C/F/K):")
        valid = ("C", "F", "K")
        if not tempin.isnumeric() or scalein not in valid or scaleout not in valid:
            print("Please reenter:")
            continue
        return int(tempin), scalein, scaleout
        
print(gettemp())