Fix quotes inside bracketed f-strings

[scauligi]

Fixes #2474.

maneuvering escapes through encodings and encodings through escapes

[Kodiologist]

You can flatten the else: if not … into elif: not ….

Why use ISO-8859-1 (a.k.a. latin1) in res.encode('latin1', errors='backslashreplace') instead of UTF-8 or ASCII? I looked at the linked answer, but it doesn't say. If you really need ISO-8859-1 for some reason, I think it's clearer to call it that than "latin1".

Looks good otherwise.

[scauligi]

The latin1 thing is because because of a python bug (python/cpython#65530); encoding to UTF-8 (or otherwise non-latin1) causes it to mess up non-ascii codepoints in the original string:

>>> r'\N{angry face} \u00fc | ü 😠'.encode().decode('unicode_escape')
'😠 ü | ü ð\x9f\x98\xa0'
>>> r'\N{angry face} \u00fc | ü 😠'.encode('latin1', 'backslashreplace').decode('unicode_escape')
'😠 ü | ü 😠'

I added a comment as well.

[Kodiologist]

A Python bug approaching the age of 10. Go figure. Thanks.