spam = ['apples', 'bananas', 'tofu', 'cats']
def commaAnd(aList):
    aList.insert(-1, 'and')
    together = aList[0]                 #adds the first word without comma
    for i in range(len(aList) - 2):     #-2 so that a comma does not follow 'and'
        together = together + ', ' + aList[i + 1]   #adds commas after first word
    together = together + ' ' + aList[-1]           #adds last word without comma
    print(together)
commaAnd(spam)