Ex

spam = ['apples', 'bananas', 'tofu', 'cats']

def comma(a_list):
    last = a_list[-1]
    all_but_last = a_list[0:-1]
    result = ''
    for item in all_but_last:
        result += item
        result += ', '
    result += 'and '
    result += all_but_last
    print(result)


comma(spam)