Automate the boring stuff with Python: Comma Code

Question

Currently working my way through this beginners book and have completed one of the practice projects \'Comma Code\' which asks the user to construct a program which:

Answer 1

I came up with this solution

#This is the list which needs to be converted to String
spam = ['apples', 'bananas', 'tofu', 'cats']

#This is the empty string in which we will append
s = ""


def list_to_string():
    global spam,s
    for x in range(len(spam)):
        if s == "":
            s += str(spam[x])
        elif x == (len(spam)-1):
            s += " and " + str(spam[x])
        else:
            s += ", " + str(spam[x])
    return s

a = list_to_string()
print(a)