Write a Python program to find the first repeated word in a given string

def first_repeated_word(str1):
  temp = set()
  for word in str1.split():
    if word in temp:
      return word;
    else:
      temp.add(word)
  return 'None'
print(first_repeated_word("ab ca bc ab"))
print(first_repeated_word("ab ca bc ab ca ab bc"))
print(first_repeated_word("ab ca bc ca ab bc"))
print(first_repeated_word("ab ca bc"))