CS50P-pset5-test_fuel: My code for fuel.py did not raise ZeroDivisionError

Question

My code for fuel.py:

def main():
    while True:
        # Prompting the user to enter a fraction
        fraction = input("Fraction: ")

        # Calling check_fraction() function to validate the input
        x, y = convert(fraction)

        # If x or y is None, prompting the user again to enter a valid fraction
        if x is None or y is None:
            continue

        # Calculating the percentage of the fraction
        percentage = int(round(x / y * 100))

        # Output E if the percentage is less than or equal to 1
        if percentage <= 1:
            print(gauge(percentage))
        # Output F if the percentage is greater than or equal to 99
        elif percentage >= 99:
            print(gauge(percentage))
        # Output the percentage as a percentage value
        else:
            print(f"{gauge(percentage)}%")
        break

def convert(fraction):
    try:
        # Splitting the fraction by '/' and convert the values to integers
        x, y = map(int, fraction.split("/"))

        # Raising ValueError if x is greater than y or y is less than or equal to zero
        if x > y or not str(x).isnumeric() or not str(y).isnumeric() or y==0:
            # Returning None for x and y if an exception is raised
            return None, None
        #frac=x/y I included this line to create  a situation for ZeroDivisionError, but it did not work

        # Returning x and y if the fraction is valid
        return x, y

    # Handle ValueError and ZeroDivisionError exceptions
    except (ValueError, ZeroDivisionError):
        raise

def gauge(percentage):
    if percentage <= 1:
        return "E"
    elif percentage >= 99:
        return "F"
    else:
        return percentage


if __name__ == "__main__":
    main()

My code for checking ZeroDivisionError in test_fuel.py:

def test_zero_division():
    with pytest.raises(ZeroDivisionError):
        fuel.convert("5/0")

Answer 1

Short answer: you don't raise a ValueError because you have return None, None in this code block when you catch y==0:

if x > y or not str(x).isnumeric() or not str(y).isnumeric() or y==0:
    # Returns None for x and y when logic above is True
    return None, None

Use a try/except block to raise exceptions. try/except "tries" to execute the line(s) of code after the try: statement and continues silently if there are no errors. The except: block is only executed if there is an error. That's where you raise the appropriate exception.

Something like this would work to catch the divide by zero error when y=0:

# Raise ZeroDivisionError if y is zero
try:
    frac = x/y 
except:
    raise ZeroDivisionError

Ideally you have try/except blocks to catch each exception you want to raise. In other words, 1 for the map()/split function, and another for divide by zero.

Also, you need to add some try/except logic in main() to handle exceptions when they are raised by convert(). Otherwise you will just get an ugly traceback with the exception. :-)