可变对象和不可变对象

def solve():
    x = [1]
    y = x
    x += [2]
    lf = 'list_same' if y is x else 'list_new'
    s = 'ab'
    t = s
    s = s + 'c'
    sf = 'str_same' if t is s else 'str_new'
    return f'{lf},{sf}'