On Thu, Jun 10, 2021 at 7:10 AM Chris Angelico <rosuav@gmail.com> wrote:
This proposal is basically for a way to take an f-string-like construct and, instead of calling format() on each of the values and joining them together into a string, you do something else with it. Or from a language perspective, you package it all up and hand it to a custom function.
So it's basically an f-string minus the final step - which is why PEP 501 described f-strings in terms of interpolated strings.
Unevaluated f-strings is a nice way to think about this functionality. Another use-case that comes to mind is logging. The Google Python style guide says not to use f-strings, for example, because it wants to be able to collect the unexpanded pattern strings and not waste time rendering unlogged messages: https://google.github.io/styleguide/pyguide.html#3101-logging