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.

[DeaD_EyE]

def test():
 return [1, 2, 3, 4, 5]
 
 
def test2():
    return [6, 7, 8, 9, 10]
 

def test3():
    return [11, 12, 13, 14, 15]


final_list = test1() + test2() + test3()
print()
print(final_list)

[buran]

to elaborate further, based on DeaD_EyE's exmaple:
you can also assign what a function has returned to a variable to preserve and use latter in the code

my_list = test()

[ka06059]

if we replace the outside list from None to []... then append it inside function, should work the same. no parameters,return or global keywords needed. list id also preserved. jz repeat the same for test2() and test3(). did this in python 2.7 just in case error occured

list = []

def test():
 for a in range(1,6):
    list.append(a)
test()

Output:
list = [1,2,3,4,5]

[buran]

OP wants to avoid using global variable (good).
Your code is poor because it uses global variable, change it using mutability of list and uses built-in function list() as variable name. Don't do this...

[ka06059]

thx, will keep in mind on that variabe name

if preserving id is the reason im using global variable...
OP uses global variable , yet the list id changed , same goes to my_list = test()
so either way we end up using global variable?

[buran]

the idea is to keep namespaces separated and the scope of variables as narrow as possible. in the OP original code and your code you mix the global module namespace and the local function namespace

[digitalmatic7]

def test():
 return [1, 2, 3, 4, 5]
 
 
def test2():
    return [6, 7, 8, 9, 10]
 

def test3():
    return [11, 12, 13, 14, 15]


final_list = test1() + test2() + test3()
print()
print(final_list)

I appreciate the help once again, DeaD_EyE !

I think I understand 'return' well enough to use it in my projects now.

Part of my confusion was passing multiple objects into a single return, then combining them outside the function, but it seems easy in this case (multiple lists I want to combine). I'm still not 100% sure how to return different object types, like for example a string and a list through return, because then it's like they're combined into a single variable when you call the function.

Is the rule to only return 1 kind of data per function?

def test1():

    link_list1 = [1, 2, 3, 4, 5]
    link_list2 = [6, 7, 8, 9, 10]
    link_list3 = [11, 12, 13, 14, 15]

    return link_list1 + link_list2 + link_list3


def test2():

    link_list4 = [16, 17, 18, 19, 20]
    link_list5 = [21, 22, 23, 24, 25]
    link_list6 = [26, 27, 28, 29, 30]

    return link_list4 + link_list5 + link_list6


final_list = test1() + test2()
print()
print(final_list)

This forum is the best, its helped me overcome all the brick walls I've hit so far, you guys are amazing.

[buran]

you can return anything (i.e. any object), incl. some complex data structure like list/tuple of mixed element types, or dict, etc.

[DeaD_EyE]

You can return everything:

def foo():
    return {}, 'Foo', 42, 1337.13, [], ()

Implicit all arguments are packed into a tuple.
Afterwards you can unpack the objects.

Dict, String, Integer, Float, List, Tuple = foo()

Now the names refer to the objects.