Find the first repeated wordΒΆ

Find the first repeated word in a given string.
def first_repeated_word(S):

    temp = set()

    for word in S.split():
        if word in temp:
            return word
        else:
            temp.add(word)

  return 'None'

# test
print(first_repeated_word("ab ca bc ab"))             # ab
print(first_repeated_word("ab ca bc ab ca ab bc"))    # ab
print(first_repeated_word("ab ca bc ca ab bc"))       # ca
print(first_repeated_word("ab ca bc"))                # None