def common_words_filter(my_string_1, my_string_2):

   my_word_count = {}

   for word in my_string_1.split():
      my_word_count[word] = my_word_count.get(word, 0) + 1

   for word in my_string_2.split():
      my_word_count[word] = my_word_count.get(word, 0) + 1

   return [word for word in my_word_count if my_word_count[word] == 1]

my_string_1 = "Python is fun"
print("第一个字符串是：")
print(my_string_1)

my_string_2 = "Python is fun to learn"
print("第二个字符串是：")
print(my_string_2)

print("结果是：")
print(common_words_filter(my_string_1, my_string_2))

第一个字符串是：
Python is fun
第二个字符串是：
Python is fun to learn
两个字符串中不共有的单词是：
['to', 'learn']