8.Part of the Whole - 'int' 'NoneType' error


#1



https://www.codecademy.com/courses/python-beginner-en-qzsCL/1/4?curriculum_id=4f89dab3d788890003000096


Oops, try again. get_class_average([alice]) resulted in an error: unsupported operand type(s) for +: 'int' and 'NoneType'


I dont untderstand the error message: What is an operand type?
What means 'int' and 'NoneType' in this context?

Well, I also dont get what is wrong with the code, so even after going through a few posts I still dont see the solution.

Glad for your help!


lloyd = {
    "name": "Lloyd",
    "homework": [90.0, 97.0, 75.0, 92.0],
    "quizzes": [88.0, 40.0, 94.0],
    "tests": [75.0, 90.0]
}
alice = {
    "name": "Alice",
    "homework": [100.0, 92.0, 98.0, 100.0],
    "quizzes": [82.0, 83.0, 91.0],
    "tests": [89.0, 97.0]
}
tyler = {
    "name": "Tyler",
    "homework": [0.0, 87.0, 75.0, 22.0],
    "quizzes": [0.0, 75.0, 78.0],
    "tests": [100.0, 100.0]
}

# Add your function below!
def average(numbers):
    total = sum(numbers)
    total = float(total)
    total = total / len(numbers)
    return total

print average(lloyd['homework'])

def get_average(student):
    homework = average(student['homework'])
    quizzes = average(student['quizzes'])
    tests = average(student['tests'])
    avg_grade = 0.1 * homework + 0.3*quizzes + 0.6*tests
    print student['name']
    print avg_grade
    
    
print get_average(lloyd)

def get_letter_grade(score):
    if score >= 90:
        return 'A'
    elif score >= 80:
        return 'B'
    elif score >= 70:
        return 'C'
    elif score >= 60:
        return 'D'
    else:
        return 'F'


def get_class_average(students):
    results = []
    for student in students:
        get_average(student)
        results.append(get_average(student))
    return average(results)


#2

Hi @niknik88,

What does the get_average function return?


#3

omg, thank you :smiley:
I played around with the code later on and didnt realize it wouldnt return anything after that.

Could you explain the error code to me? I feel like the more I know about them the easier I can track down my mistake.


#4

Without having a return statement, the get_average function returned None when the get_class_average function called it here ...

    results.append(get_average(student))

As a consequence, results became a list of NoneType objects.

Then, the get_class_average function passed results to the average function here ...

    return average(results)

The error message indicated that the sum function that you called here, within the average function ...

    total = sum(numbers)

... could not add up NoneType objects. To create a total, we start with 0, which is an int. Thereafter, we can use the + or the += operator to accumulate numbers in the total. However, we cannot add None to the total.

EDITED (February 26, 2017) to add the following ...

Here's a little experiment to confirm what happens if we pass a list of NoneType objects to the sum function ...

print(sum([None, None]))

Part of error message ...

TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

#5

THAT was really really helpful!! Thank you!!


#6