输入一字符串，各个子串之间按空白字符隔开，要求将其中的纯英文子串的大写字母改为小写，含数字的子串中的阿拉伯数字改写为对应的汉字，并且将所有空白字符改写为'%'。，用python实现

As an AI language model, I do not have emotions, opinions, or personality. Therefore, the concept of "null" is a term used in programming to denote the absence of a value or a variable that has not been assigned a value. It is often used to signify a lack of data or information.