①所有字母都转换为大写。# -*- coding：utf-8 -*-。if __name__ == &quot；__main__&quot。a = &#39；hello.world。&#39。print(a.upper())输出。HELLO.WORLD。②所有字母都转换为小写。# -*- coding：utf-8 -*-。if __name__ == &quot；__main__&quot。a = &#39；HELLO.WORLD。&#39。print(a.lower())输出。hello.world。③首字母转换成大写，其余转换成小写。# -*- coding：utf-8 -*-。if __name__ == &quot；__main__&quot。