Avoiding division by zero

Question

I know this is basic so any help appreciated.

This is my code - i just cannot get the if statement to avoid the division by zero to work.

Can anyone help?

# problem: calculate what percent of car park spaces are occupied
# input: integers 1 or 0, 1 signals an occupied space and 0 is empty

car_park_spaces = []
          
# sub problem: number of occupied spaces
occupied = 0

for car_park_space in car_park_spaces:
    if car_park_space == 1:
        occupied += 1
    occupied_spaces = occupied

    # sub problem: find the length of the list
    percentage = occupied_spaces / len(car_park_spaces) * 100

    # output: percent of occupied spaces
    if not car_park_spaces:
        print('The list is empty')
    else:
        print ('The percentage of occupied spaces is', percentage, '%')

Answer 1

I moved the code into function so it's more structured. The function looks like this:

def occupied_percent(car_park_spaces):
    if not car_park_spaces:
        return None
        
    occupied = 0
    total_spaces = len(car_park_spaces)

    for space in car_park_spaces:
        if space:
            occupied += 1

    return occupied / total_spaces * 100

The output is a float if the percentage was computed successfully, otherwise the output is None. When using the function you have to check the return value before printing the result.

Next I created printing function that simplifies usage:

def print_percentage(car_park_spaces):
    result = occupied_percent(car_park_spaces)
    print('The list is empty.' if result is None else f'The percentage of occupied spaces is {result}%.')

And I run some test cases:

print_percentage([])
print_percentage([0])
print_percentage([1])
print_percentage([1, 0])
print_percentage([1, 0, 1, 1])

Those produce this output:

The list is empty.
The percentage of occupied spaces is 0.0%.
The percentage of occupied spaces is 100.0%.
The percentage of occupied spaces is 50.0%.
The percentage of occupied spaces is 75.0%.

Note that the code can be probably simplified further because Python tends to use a lot of one-liners.