I am trying to make a function that prints the variance of a list of defined numbers:
grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
So far, I have tried proceeding on making these three functions:
def grades_sum(my_list):
total = 0
for grade in my_list:
total += grade
return total
def grades_average(my_list):
sum_of_grades = grades_sum(my_list)
average = sum_of_grades / len(my_list)
return average
def grades_variance(my_list, average):
variance = 0
for i in my_list:
variance += (average - my_list[i]) ** 2
return variance / len(my_list)
When I try to execute the code, however, it gives me the following error at the following line:
Line: variance += (average - my_list[i]) ** 2
Error: list index out of range
Apologies if my current Python knowledges are limited, but I am still learning - so please if you wish to help solving this issue try not to suggest extremely-complicated ways on how to solve this, thank you really much.
First I would suggest using Python's built-in sum method to replace your first custom method. grades_average then becomes:
def grades_average(my_list):
sum_of_grades = sum(my_list)
average = sum_of_grades / len(my_list)
return average
Second, I would strongly recommend looking into the NumPy library, as it has these methods built-in. numpy.mean() and numpy.std() would cover both these cases.
If you're interested in writing the code for yourself first, that's totally fine too. As for your specific error, I believe @gnibbler above nailed it. If you want to loop using an index, you can restructure the line in grades_variance to be:
for i in range(0, len(my_list)):
As Lattyware noted, looping by index is not particularly "Pythonic"; the way you're currently doing it is generally superior. This is just for your reference.