How can I compute a sum from the grades_input?
Rather than computing a sum with another loop, we can make use of the function we made in the previous step: grades_sum(). If we create some variable to hold the sum of the input list, grades_input, we can assign it a value by doing our_variable = grades_sum(grades_input).
After that, computing the average can be done by following the instructions and ensuring that you make the average a float!
When i did this exercise i tried running it with out the float function and got the exact same result ‘80.4230769231’.
Despite that it failed me with the message ‘grades_average([8, 9, 4, 1, 9, 2]) returned 5 instead of the expected: 5.5’.
Why does this matter?
Maybe this article explains why. It says:
In Python 2.7, the “/” operator works as a floor division for integer arguments. However, the operator / returns a float value if one of the arguments is a float (this is similar to C++)
So we have to transform an integer into float to get a float result. This is different from Python 3, by the way.
The simple fact that one of your scores was a decimal (the 50.5) automagically got you the floating result THIS TIME.
Putting the float function in insures you get a floated answer (with a decimal), instead of a rounded/ floored/integer answer.
(It appears that Codecademy background tests our coding with their own input values ----- all integers, according to your error notice ------sneaky bums 
)
why in this case does sum_of_grades = grades_sum(grades_input) have grades_input as a argument to call it?
You are calling the function that you did before: grades_sum().
So you are telling that you need the grades_sum of your grades_input, and saving it as sum_of_grades.
Hope you can understand me:)