Case insensitive replacement?

[MRAB]

On 2016-09-27 17:56, Tim Chase wrote:
> I'd like to do a case-insensitive replacement in a string but want to
> do it pythonically.  Ideally, the code would something like
>
>   needle = "World"
>   haystack = "Hello, world!"
>   replacement = "THERE"
>   result = haystack.replace(needle, replacement, ignore_case=True)
>   # result would be "Hello, THERE!"
>
> As that's not an option, I can do it either with string-hacking:
>
>   try:
>     index = haystack.upper().find(needle.upper())
>   except ValueError:
>     result = haystack
>   else:
>     result = (
>       haystack[:index]
>       + replacement
>       + haystack[index + len(needle):]
>       )
>
The disadvantage of your "string-hacking" is that you're assuming that 
the uppercase version of a string is the same length as the original:

That's not always the case:

Python 3.5.1 (v3.5.1:37a07cee5969, Dec  6 2015, 01:54:25) [MSC v.1900 64 
bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> '\N{LATIN SMALL LETTER SHARP S}'
'ß'
 >>> '\N{LATIN SMALL LETTER SHARP S}'.upper()
'SS'
 >>>

> or with regexes:
>
>   import re
>   r = re.compile(re.escape(needle), re.I)
>   result = r.sub(replacement, haystack)
>
> The regex version is certainly tidier, but it feels a bit like
> killing a fly with a rocket-launcher.
>
> Are there other/better options that I've missed?
>
> Also, if it makes any difference, my replacement in this use-case is
> actually deletion, so replacement=""
>