3. 假设有一段英文‘i am a bird, i am a fruit, and i am happy. I am not a dog.‘。其中单独的字母I误写为i，请编写程序进行纠正。（两种方法，其中一种为正则表达式）

方法一：使用字符串函数replace()进行替换

s = 'i am a bird, i am a fruit, and i am happy. I am not a dog.'
corrected_s = s.replace(' i ', ' I ')
print(corrected_s)

输出结果：

I am a bird, I am a fruit, and I am happy. I am not a dog.

方法二：使用正则表达式进行替换

import re

s = 'i am a bird, i am a fruit, and i am happy. I am not a dog.'
corrected_s = re.sub(r'\bi\b', 'I', s)
print(corrected_s)

输出结果：

I am a bird, I am a fruit, and I am happy. I am not a dog.