Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.38%. Comparing base (83131c1) to head (c734ae9).
⚠️ Report is 37 commits behind head on master.

@@           Coverage Diff           @@
##           master   #18495   +/-   ##
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  Coverage   98.38%   98.38%           
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  Files         171      171           
  Lines       22301    22301           
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  Hits        21940    21940           
  Misses        361      361           

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When I read 'nested' I thought this was about f"{f'{1}'}" (which Micropython does not support but with a cryptic 'TypeError: 'str' object isn't callable' error.)

Nitpick: perhaps this should be named 'f-string with nested brackets' ?

When I read 'nested' I thought this was about f"{f'{1}'}" (which Micropython does not support but with a cryptic 'TypeError: 'str' object isn't callable' error.)

Nitpick: perhaps this should be named 'f-string with nested brackets' ?

Good idea. I re-titled and re-worded, but I used the term "curly braces" same as the cpython documentation.

used the term "curly braces" same as the cpython documentation

Thanks, makes sense. Can you change it in the comment on the test as well?

I've revised yet again what this test fragment explains it is testing. The CPython docs end up explaining it like this:

Top-level format specifiers may include nested replacement fields. These nested fields may include their own conversion fields and format specifiers, but may not include more deeply nested replacement fields. The format specifier mini-language is the same as that used by the str.format() method.

This is different than the following cases of nested curly braces: f"{{ }}" (doubled curly braces, whether matched or not, indicate single literal curly braces in the output) and f{ {3}} (a set literal inside an f-string replacement field) and are already tested.

Rebased and merged in ef567dc