The bistring library provides non-destructive versions of common string processing operations like normalization, case folding, and find/replace. Each bistring remembers the original string, and how its substrings map to substrings of the modified version.
For example:
>>> from bistring import bistr
>>> s = bistr('𝕿𝖍𝖊 𝖖𝖚𝖎𝖈𝖐, 𝖇𝖗𝖔𝖜𝖓 🦊 𝖏𝖚𝖒𝖕𝖘 𝖔𝖛𝖊𝖗 𝖙𝖍𝖊 𝖑𝖆𝖟𝖞 🐶')
>>> s = s.normalize('NFKD') # Unicode normalization
>>> s = s.casefold() # Case-insensitivity
>>> s = s.replace('🦊', 'fox') # Replace emoji with text
>>> s = s.replace('🐶', 'dog')
>>> s = s.sub(r'[^\w\s]+', '') # Strip everything but letters and spaces
>>> s = s[:19] # Extract a substring
>>> s.modified # The modified substring, after changes
'the quick brown fox'
>>> s.original # The original substring, before changes
'𝕿𝖍𝖊 𝖖𝖚𝖎𝖈𝖐, 𝖇𝖗𝖔𝖜𝖓 🦊'This allows you to perform very aggressive text processing completely invisibly.