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F-strings are great. The only downside I’ve found is they are incompatible with the stdlib logging framework’s deferred string interpolation feature (using %s style string interpolation), which can give you a nice performance boost if you make lots of expensive debug logs for tests, but run at info level in production.

That said most apps probably won’t see much of a difference in perf between the two approaches.

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f-strings are so much faster that I've seen an increase in speed over %-formatting for logging. If there's even a 10% chance that a string will be actually logged (and therefore %-formatting will take place), I'll replace it with an f-string and not care about the deferred formatting.

Here are some benchmarks and a discussion about using f-strings in logging I remember reading a few years ago:

https://github.com/PyCQA/pylint/issues/2395

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