python - How to prevent a list from changing after being used as parameter in function?

Question

I have a little code which is not outputting the result as I wanted.

Code

def func_a(list1):
    list1.insert(2,'3')
    list1.append('c')
    return (list1)

def main():
    list_1 = ['1','2','a','b']    
    list_2 = func_a(list_1)
    print (list_1)
    print ("
")
    print (list_2)

main()

Output to this code is:

['1', '2', '3', 'a', 'b', 'c']


['1', '2', '3', 'a', 'b', 'c']

I want it to be:

['1', '2', 'a', 'b']


['1', '2', '3', 'a', 'b', 'c']

Answer 1

You have to create a copy of the list, and modify that:

def func_a(list1):
    list1copy = list1[:]
    list1copy.insert(2,'3')
    list1copy.append('c')
    return (list1copy)

You could also keep func_a the same, and just call it with a copy of the list:

list_2 = func_a(list_1[:])