How to replace a word in a given sentence with a particular pattern if it's case insensitive in python?

I am given the sentence My team is the BeST team at the tournament. as a test case to create create a function

def case_insensitivity(sentence):
    return new_sentence

which checks a given sentence for a case insensitive word and replaces the case insensitive word with XXX_.

i.e.

print(case_insensitivity('My team is the BeST team at the tournament'))
result
'My team is the XXX_ team at the tournament'

What’s the best way to do this? casefold()

>Solution :

Assuming we define the target words as having both a lowercase and uppercase beyond the first character, we can try using re.sub for a regex option:

def case_insensitivity(sentence):
    return re.sub(r'\w+(?:[A-Z]\w*[a-z]|[a-z]\w*[A-Z])\w*', 'XXX_', sentence)

print(case_insensitivity('My team is the BeST team at the tournament'))

This prints:

My team is the XXX_ team at the tournament