items not appending to list, or list returning as empty in python?

Question

In my code, the item percentgrade is not appending to the list lnpercentgrade in each iteration of a for loop, but I'm not sure why. When I try to sum the items in lnpercentgrade (at the end of the code), I am returned 0 because lnpercentgrade is empy. I have lnpercentgrades declared as a global variable outside of the maininput() function, because otherwise at the bottom of the code when I try to sum(lnpercentgrades), I am returned "lnpercentgrades not defined". I'm guessing lnpercentgrades is not being modified somehow inside the maininput() function, even though I am sure I typed it correctly before the .append function. What I am really trying to do is match the sum(lnpercentgrades) with 100, but when I enter 5 items all with value of 20, the sum is 0 instead of 100. The important lines are marked with arrows <<<<<<<<<<<<<<<<<<<<< ``` lnpercentgrades = [] <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< def maininput(): numtests = int(input("Enter # of tests:")) numassign = int(input("Enter # o…

Accepted Answer

At first glance, it looks like you may have a scoping issue. You are modifying the list inside of the function, but keep in mind that is a local copy of the list. Despite the fact you are declaring it in the outer scope, you are not prefacing it with `global`, which means it instead creates a function-local copy, does its business and then exits, not affecting the 'main' list at all.

I would suggest modifying your function to return the lists you want so that you can use them as you'd expect. Here is a basic example:

```
def MyFunc():
    l1 = ['my', 'first', 'list']
    l2 = ['another', 'list']
    return l1, l2

main_list, second_list = MyFunc()

print(main_list)
print(second_list)
```

Which will output:

```
['my', 'first', 'list']
['another', 'list']
```

If you really want to keep the variable in the outer scope, you would have to preface it with `global` inside of your function (I would probably go with the first method though):

```
main_list = []
second_list = []

def MyFunc():
    global main_list
    global second_list
    main_list = ['more', 'good', 'stuff']
    second_list = ['another', 'list']

MyFunc()

print(main_list) # ['more', 'good', 'stuff']
print(second_list) # ['another', 'list']
```

items not appending to list, or list returning as empty in python?

Solution

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