string - Python string case-insensitive replacement

Question

Replace hello in Hello World, HELLO PYTHON with My.
Since the replace() function replacement is case-sensitive, how can Python implement string replacement without case sensitivity?

Answer 1

Reference article: Issues related to Python string operations

String case-insensitive replacement
str.replace(old, new[, max])The replacement is case-sensitive. Case-insensitive replacement requires the regular expression re.sub() with the re.IGNORECASE option.

>>> import re
>>> reg = re.compile(re.escape('hello'), re.IGNORECASE)
>>> reg.sub('My', 'Hello World, HELLO PYTHON')
'My World, My PYTHON'

Answer 2

import re

s = 'Hello World, HELLO PYTHON'
print re.sub(r'(?i)hello', 'My', s)