Automate the Boring Stuff Comma Code

spam=[]
def comma_code(spam):
    return 'spam[:-1]'+' and'+' spam[-1]'
while True:
    print('Please enter a list of at least two items.'+' (Or enter nothing to stop.):')
    item=input()
    if int(len(spam))< 2:
        print('Your list is too short.')
    if int(len(spam))>= 2:
        print('You have entered a valid list.')
    else:
        break
    spam=spam+ [item] # list concatenation

comma_code(spam)