How do I get my function to refer to a variable set outside of the function?

Question

When I try and use the code below, even when I run the set_list_index function it doesn't change the list_index variable. I.E. I pass it a 2 and list_index stays as a 0. I don't understand why it is failing to make this change, but it seems like it is failing to recognize the list_index variable because it is not within the function?

list = ["adam", "bob", "carmen"]
list_index = 0

def useful_function_1():
    print(1)

def set_list_index(num):
    list_index == num

def refers_to_list(num):
    print(list[num])

def print_list_index():
    print(list[list_index])

set_list_index(2)
print_list_index()

yes I thought I would be able to pass set_list_index an integer using this, should I use "int" instead of "num"? — Steve, Feb 08 '22 at 11:44
Does this answer your question? [Using global variables in a function](https://stackoverflow.com/questions/423379/using-global-variables-in-a-function) — Max, Feb 08 '22 at 12:08
@MaxMiller I would have thought so but even when I add "global list index" as the first line of set_list_index it still doesn't change list_index when I pass it a number. Maybe the issue isn't with the variable? — Steve, Feb 08 '22 at 12:17
it has to be `=` instead of `==` in `list_index = num`. And it needs `global list_index` in `set_list_index` — furas, Feb 08 '22 at 12:18
Thanks @furas it turns out that in conjunction with the global variables thing was the solution — Steve, Feb 08 '22 at 12:19
Why not *return* a value and use: `list_index = set_list_index(num)`? Using global variables is frequently a sign of poor design. — John Coleman, Feb 08 '22 at 12:36

score 0 · Answer 1 · answered Feb 08 '22 at 12:20

Step 1 to fix: define the list_index as "global" step 2: remove unneccessary second =

resulting fixed code:

list = ["adam", "bob", "carmen"]
list_index = 0

def useful_function_1():
    print(1)

def set_list_index(num):
    global list_index
    list_index = num

def refers_to_list(num):
    print(list[num])

def print_list_index():
    print(list[list_index])

set_list_index(2)
print_list_index()

How do I get my function to refer to a variable set outside of the function?

1 Answers1