Is This Code Ok? How Can I Avoid Using Global Variables?

[digitalmatic7]

I've heard from multiple sources I should try to avoid using global variables, since it's probably a sign of broken / badly written code. Here's an example of what I need to do:

list1 = None
list2 = None
list3 = None


def test():

    global list1
    list1 = [1, 2, 3, 4, 5]


def test2():

    global list2
    list2 = [6, 7, 8, 9, 10]


def test3():

    global list3
    list3 = [11, 12, 13, 14, 15]


test()
test2()
test3()

final_list = list1 + list2 + list3

print()
print(final_list)


'''

    in the full script LOTS of actions will be taken inside each function to generate the lists,
    this code is just for a very basic example of what I plan to do.

'''

I'm aware of 'return' and 'function parameters', I've been researching them in my free time today, but I can't get them to replace global variables in this situation.