Case insensitive replacement?

[Paul Rubin]

>  needle = "World"
>  haystack = "Hello, world!"
>  replacement = "THERE"
>  result = haystack.replace(needle, replacement, ignore_case=True)
>  # result would be "Hello, THERE!"

>>> import re
>>> re.sub('(?i)world','THERE','Hello World')
'Hello THERE'