关于#python#的问题：python中替换

假设有一段英文，其中有单独的字母“I”误写为“i”，请编写程序纠正。
如：i am a teacher,i am man, and i am 38 years old.I am not a businessman.
请问怎么才能不让后面单词businessman中的i也替换成I 怎么保持不变啊
附上我写的后面单词里的i也变了😭

import re
a = 'i am a teacher,i am man, and i am 38 years old.I am not a businessman.'
print(re.sub('(?<!\w)i(?!\w)','I',a))
I am a teacher,I am man, and I am 38 years old.I am not a businessman.

不能replace呀
先按空格split
然后把单独的i替换
再重新合并