Fix spurious E231 for nested f-string format specifiers#1312
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Fridayai700 wants to merge 1 commit intoPyCQA:mainfrom
Open
Fix spurious E231 for nested f-string format specifiers#1312Fridayai700 wants to merge 1 commit intoPyCQA:mainfrom
Fridayai700 wants to merge 1 commit intoPyCQA:mainfrom
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When a replacement field appears inside an f-string format spec
(e.g. `f"{x:0.{digits:d}f}"`), the `:` in the nested `{digits:d}` is a
format specifier, not a dict colon. Previously pycodestyle reported a
false-positive E231 on it because the brace-stack pattern `['f', '{']`
only matched the top-level replacement field.
Track `FSTRING_MIDDLE` / `TSTRING_MIDDLE` tokens: when `{` is opened
immediately after one of these tokens it is a nested replacement field
inside a format spec. Push `'F'` (instead of `'{'`) onto the brace
stack, then suppress E231 for `:` when the top of the stack is `'F'`.
Fixes PyCQA#1241.
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Summary
Fixes #1241. When a replacement field appears inside an f-string format spec (e.g.
f"{x:0.{digits:d}f}"), the:in the nested{digits:d}is a format specifier colon, not a dict colon. Previously pycodestyle reported a false-positive E231 on it.The fix tracks
FSTRING_MIDDLE/TSTRING_MIDDLEtokens: when{is opened immediately after one of these tokens, it is a nested replacement field inside a format spec. A distinct marker'F'(instead of'{') is pushed onto the brace stack, and E231 is suppressed for:when the top of the stack is'F'.Test plan
testing/data/python312.py:f"{x:0.{digits:d}f}"— the exact reproducer from Spurious E231 for nested format substitutions #1241f'{value:{fill}{align}{width}.{precision}f}'— multiple nested fields in format specf"{ {'a':'b'} }") still correctly trigger E231