How to calculate user input in python

Question

I am supposed to write a program in Python that asks for grades one at a time. When the user enters “done” , calculate the following: grade average.

This is what I have so far:

def main():
    user_input = input("Enter grade: ") 
    number = user_input
    while True:
        user_input = input("Enter grade: ")
        if user_input == "done":
            break
    avg(number)

def avg(a):
    average = sum(a)/len(a)
    print(average)

if __name__ == "__main__":
    main()

Whenever I enter "done," the program gives me this error.

TypeError: 'int' object is not iterable

I have tried changing the user_input variable to :

user_input = int(input("Enter grade: "))

But, another error: TypeError:

'int' object is not iterable user input

I am extremely new to programming. Can anyone help me work this out? I have been searching online for the past two hours and have not found anything that did not just produce another error.

Welcome to SO. There's quite a few questions pretty much exactly like this already, so you should probably do a search first. E.g. stackoverflow.com/questions/19190739/user-input-average, or stackoverflow.com/questions/12539934/…. — user1425689
– user1425689, Commented Oct 7, 2016 at 16:22

N4v · Accepted Answer · 2016-10-07 16:25:09Z

1

I am noticing some things which may solve the issue for you.

You're feeding number to the avg function when really you want to give it a list of numbers.
I think you should do something like this: make a list called numbers and append each user input to that list. Then use the avg function on the numbers list.

answered Oct 7, 2016 at 16:25

N4v

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Comments

Chris · Accepted Answer · 2016-10-07 17:25:42Z

There are a few flaws in your logic.

Each time you ask for user input in main(), you override the value of user_input. What you should be doing, is gathering each numbers in a list().
What the errors Python raised are telling you, is that the builtin function sum(), takes a list of numbers, not a single number, which your passing in.
the input() function returns a string, so you need to convert the input to a integer.

I would rewrite your program as the following:

def main():
    # create a list to store each grade
    # that the user inputs.
    grades = []

    # while forever
    while True:
        # get input from the user.
        # I am not converting the input to a integer
        # here, because were expecting the user to
        # enter a string when done.
        i = input("Enter grade: ") 

        # if the user enters 'done' break the loop.
        if i == 'done':break 

        # add the grade the user entered to our grades list.
        # converting it to an integer.
        grades.append(int(i)) 

    # print the return value 
    # of the avg function.
    print("Grade average:", avg(grades))

def avg(grades):
    # return the average of 
    # the grades.
    # note that I'm using the builtin round()
    # function here. That is because
    # the average is sometimes a 
    # long decimal. If this does not matter 
    # to you, you can remove it.
    return round(sum(grades)/len(grades), 2)

# call the function main()
main()

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