[Solved] Python looping code

Question

You miss the lines

if grade != -1:
    numbers.append(grade)

after grade = int(grade). This adds the grade to the list numbers.

Review

Use PEP8 (you can use pep8online.com) to check your code
For unnamed input, I prefer "Largest is %i, smallest is %i" % (max(numbers), min(numbers))
You can use sum to sum up integers in a list
If you add a shebang (the first line #!/usr/bin/env python), then Linux users can execute your script directly like this: ./yourscript.py instead of python yourscript.py.

Code

I would rather write the code like this:

#!/usr/bin/env python


def get_grades():
    """Return a list of grades."""
    numbers = []
    while True:
        grade = int(input("Enter grade, -1 to end: "))
        if grade != -1:
            numbers.append(grade)
        else:
            return numbers


if __name__ == '__main__':
    grades = get_grades()
    if len(grades) != 0:
        average = float(sum(grades)) / len(grades)
        print('Largest is %i, smallest is %i.' % (max(grades), min(grades)))
        print("Class average is %0.2f." % average)

Reading error messages

You probably had the following:

$ python test.py 
Enter grade, -1 to end:1
Enter grade, -1 to end: 2
Enter grade, -1 to end: 3
Enter grade, -1 to end: -1
Traceback (most recent call last):
  File "test.py", line 15, in <module>
    print('Largest is {}, smallest is {}'.format(max(numbers), min(numbers)))
ValueError: max() arg is an empty sequence

Now you should first look for line number. This one says in line 15 is something wrong. This is:

print('Largest is {}, smallest is {}'.format(max(numbers), min(numbers)))

Now you have to investigate further. What exactly is wrong? What could possibly go wrong in this line?

Now you read

ValueError: max() arg is an empty sequence

That should look strange, because you checked gradeCounter != 0. Next, you would print the contents of the argument of max. This is empty, so adding to the list numbers did not work.

Accepted Answer