Sounds like a bug in your formatter, if it's meant to just do formatting but actually replaces valid syntax with invalid.

I don't totally disagree. My company uses the black formatter, which does this[0]. There are flags to skip string formatting, but is frowned upon at my organization.

[0] https://github.com/psf/black/blob/master/docs/the_black_code...

For what it's worth, black appears to do a reasonable thing and preserves the semantics of your quoted strings (as is promised by the documentation):

  $ echo "'foo'" | black -
  "foo"
  
  $ echo "'foo[\"bar\"]'" | black -
  'foo["bar"]'

  $ echo "'foo[\"bar\"]+\\'baz\\''" | black -
  "foo[\"bar\"]+'baz'"