add to a string variable without deleting last assignment

strings = None
def test(a)

       strings = str(strings) +  f"{a} \n"

when this function is called multiple times

test("hello")
test("world")

how do I allow strings to be equal to

"hello" \n
"world"

At the moment it just picks up the last time a was passed so strings is "world"

>Solution :

Try:

strings = ""

def test(a):
    global strings
    strings  +=  f"{a} \n"

test("hello")
test("world")

print(strings)