`pyupgrade` is not idempotent: upgrading %-formatting to f-strings takes two passes.

$ echo '"%s, %r" % (x, y)' > example.py

$ pyupgrade --py36-plus example.py 
Rewriting example.py

$ cat example.py 
"{}, {!r}".format(x, y)

$ pyupgrade --py36-plus example.py
Rewriting example.py

$ cat example.py
f"{x}, {y!r}"

I think this is probably just a matter of pass ordering, and would be fixed if the percent-formatting fixer ran before the f-strings fixer?

[asottile]

shed’s also in unsupported territory 😛

[Zac-HD]

Ah, I hadn’t considered it a ‘substantial portion’ since it’s really just some regex patterns and the textwrap logic, both rewritten, and there are notes in the readme and code comments. If you have a suggested form of attribution I’d be very happy to add it though!