Make a function that takes two strings as input, and outputs the common characters

Question

good day people, Please kindly assist.
Note: my answer should not allow someone to input anything.

My Attempt below i asked for an input, so please assist in providing me with another solution:

user_str_1 = input("Input String 1: ")

user_str_2 = input("Input String 2: ")

s1 = set(user_str_1)

s2 = set(user_str_2)

lst = list(s1 & s2)

print(" Common letters: {}" .format(lst))