Avoid emitting multi-line f-string elements before Python 3.12 by charliermarsh · Pull Request #24377 · astral-sh/ruff

charliermarsh · 2026-04-02T20:58:45Z

Summary

See: #24355 (comment). Prior to Python 3.12, we need to avoid emitting formatted expressions that span multiple lines in non-triple quoted f-strings.

astral-sh-bot · 2026-04-02T21:08:36Z

`ruff-ecosystem` results

Formatter (stable)

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Formatter (preview)

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charliermarsh · 2026-04-02T21:08:56Z

+```python
+if f"aaaaaaaaaaa {[ttttteeeeeeeeest]} more {
+    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+}":


This is actually invalid on Python 3.11, but the input is already invalid in this case, so I think it's within the bounds of the formatter contract?

MichaReiser · 2026-04-03T13:32:01Z

I'll review on Tuesday. What's the underlying issue here. Is it that the formatter sometimes formats an interpolation over multiple lines if the f-string contains another multiline interpolation?

charliermarsh · 2026-04-03T14:10:41Z

Is it that the formatter sometimes formats an interpolation over multiple lines if the f-string contains another multiline interpolation?

Yeah that's right. So I'm unclear if we actually consider this a bug, because I think the code has to be syntactically invalid already in order for this to trigger? In other words, we're introducing another syntax error, but the code was already invalid in another interpolation.

MichaReiser · 2026-04-03T16:03:52Z

Yeah. I guess it does make it worse. I was mainly curious to understand how rigorous we need to be (e.g. can a triple quoted f-string that's nested in a single quoted f-string contain newlines?)

charliermarsh · 2026-04-03T16:08:53Z

Thinking about it more, I'm sort of inclined to just treat this as a wontfix. I don't know that it's worth the time / concern / complexity.

dylwil3 · 2026-04-03T17:57:57Z

This warning in the formatter tests seems to implicitly say it's okay to have syntax errors if they were also present in the source:

ruff/crates/ruff_python_formatter/tests/fixtures.rs

Lines 494 to 497 in ee90846

    
                       let sub = SubDiagnostic::new( 
        
                           SubDiagnosticSeverity::Warning, 
        
                           "Only accept new syntax errors if they are also present in the input. \ 
        
                               The formatter should not introduce syntax errors.",

So I think wontfix makes sense. (Are we even technically adding a new syntax error? Or just making the existing one "worse"?)

MichaReiser

I'm fine either way and agree that I don't consider this a bug, but not introducing more syntax errors seems preferable, and the added complexity is limited.

Thank you

@charliermarsh

##### [\`v0.15.10\`](https://github.com/astral-sh/ruff/blob/HEAD/CHANGELOG.md#01510) Released on 2026-04-09. ##### Preview features - \[`flake8-logging`] Allow closures in except handlers (`LOG004`) ([#24464](astral-sh/ruff#24464)) - \[`flake8-self`] Make `SLF` diagnostics robust to non-self-named variables ([#24281](astral-sh/ruff#24281)) - \[`flake8-simplify`] Make the fix for `collapsible-if` safe in `preview` (`SIM102`) ([#24371](astral-sh/ruff#24371)) ##### Bug fixes - Avoid emitting multi-line f-string elements before Python 3.12 ([#24377](astral-sh/ruff#24377)) - Avoid syntax error from `E502` fixes in f-strings and t-strings ([#24410](astral-sh/ruff#24410)) - Strip form feeds from indent passed to `dedent_to` ([#24381](astral-sh/ruff#24381)) - \[`pyupgrade`] Fix panic caused by handling of octals (`UP012`) ([#24390](astral-sh/ruff#24390)) - Reject multi-line f-string elements before Python 3.12 ([#24355](astral-sh/ruff#24355)) ##### Rule changes - \[`ruff`] Treat f-string interpolation as potential side effect (`RUF019`) ([#24426](astral-sh/ruff#24426)) ##### Server - Add support for custom file extensions ([#24463](astral-sh/ruff#24463)) ##### Documentation - Document adding fixes in CONTRIBUTING.md ([#24393](astral-sh/ruff#24393)) - Fix JSON typo in settings example ([#24517](astral-sh/ruff#24517)) ##### Contributors - [@charliermarsh](https://github.com/charliermarsh) - [@dylwil3](https://github.com/dylwil3) - [@silverstein](https://github.com/silverstein) - [@anishgirianish](https://github.com/anishgirianish) - [@shizukushq](https://github.com/shizukushq) - [@zanieb](https://github.com/zanieb) - [@AlexWaygood](https://github.com/AlexWaygood) ##### [\`v0.15.9\`](https://github.com/astral-sh/ruff/blob/HEAD/CHANGELOG.md#0159) Released on 2026-04-02. ##### Preview features - \[`pyflakes`] Flag annotated variable redeclarations as `F811` in preview mode ([#24244](astral-sh/ruff#24244)) - \[`ruff`] Allow dunder-named assignments in non-strict mode for `RUF067` ([#24089](astral-sh/ruff#24089)) ##### Bug fixes - \[`flake8-errmsg`] Avoid shadowing existing `msg` in fix for `EM101` ([#24363](astral-sh/ruff#24363)) - \[`flake8-simplify`] Ignore pre-initialization references in `SIM113` ([#24235](astral-sh/ruff#24235)) - \[`pycodestyle`] Fix `W391` fixes for consecutive empty notebook cells ([#24236](astral-sh/ruff#24236)) - \[`pyupgrade`] Fix `UP008` nested class matching ([#24273](astral-sh/ruff#24273)) - \[`pyupgrade`] Ignore strings with string-only escapes (`UP012`) ([#16058](astral-sh/ruff#16058)) - \[`ruff`] `RUF072`: skip formfeeds on dedent ([#24308](astral-sh/ruff#24308)) - \[`ruff`] Avoid re-using symbol in `RUF024` fix ([#24316](astral-sh/ruff#24316)) - \[`ruff`] Parenthesize expression in `RUF050` fix ([#24234](astral-sh/ruff#24234)) - Disallow starred expressions as values of starred expressions ([#24280](astral-sh/ruff#24280)) ##### Rule changes - \[`flake8-simplify`] Suppress `SIM105` for `except*` before Python 3.12 ([#23869](astral-sh/ruff#23869)) - \[`pyflakes`] Extend `F507` to flag `%`-format strings with zero placeholders ([#24215](astral-sh/ruff#24215)) - \[`pyupgrade`] `UP018` should detect more unnecessarily wrapped literals (UP018) ([#24093](astral-sh/ruff#24093)) - \[`pyupgrade`] Fix `UP008` callable scope handling to support lambdas ([#24274](astral-sh/ruff#24274)) - \[`ruff`] `RUF010`: Mark fix as unsafe when it deletes a comment ([#24270](astral-sh/ruff#24270)) ##### Formatter - Add `nested-string-quote-style` formatting option ([#24312](astral-sh/ruff#24312)) ##### Documentation - \[`flake8-bugbear`] Clarify RUF071 fix safety for non-path string comparisons ([#24149](astral-sh/ruff#24149)) - \[`flake8-type-checking`] Clarify import cycle wording for `TC001`/`TC002`/`TC003` ([#24322](astral-sh/ruff#24322)) ##### Other changes - Avoid rendering fix lines with trailing whitespace after `|` ([#24343](astral-sh/ruff#24343)) ##### Contributors - [@charliermarsh](https://github.com/charliermarsh) - [@MichaReiser](https://github.com/MichaReiser) - [@tranhoangtu-it](https://github.com/tranhoangtu-it) - [@dylwil3](https://github.com/dylwil3) - [@zsol](https://github.com/zsol) - [@renovate](https://github.com/renovate) - [@bitloi](https://github.com/bitloi) - [@danparizher](https://github.com/danparizher) - [@chinar-amrutkar](https://github.com/chinar-amrutkar) - [@second-ed](https://github.com/second-ed) - [@getehen](https://github.com/getehen) - [@Redovo1](https://github.com/Redovo1) - [@matthewlloyd](https://github.com/matthewlloyd) - [@zanieb](https://github.com/zanieb) - [@InSyncWithFoo](https://github.com/InSyncWithFoo) - [@RenzoMXD](https://github.com/RenzoMXD) Renovate-Branch: renovate/2024.6-ruff-0.15.x Change-Id: Id4bd542d4f128b509284d9dcda312f2b39c29964 Priv-Id: 28ebcacdeffa50cec7a52eee59091a75ca5e9539

charliermarsh added bug Something isn't working formatter Related to the formatter labels Apr 2, 2026

charliermarsh mentioned this pull request Apr 2, 2026

Reject multi-line f-string elements before Python 3.12 #24355

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charliermarsh force-pushed the charlie/formatter-multiline branch from 1ac515a to 2af1535 Compare April 2, 2026 21:08

charliermarsh commented Apr 2, 2026

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charliermarsh marked this pull request as ready for review April 2, 2026 21:09

charliermarsh requested a review from MichaReiser as a code owner April 2, 2026 21:09

charliermarsh force-pushed the charlie/parser-multiline branch from 03d8338 to da1acf5 Compare April 3, 2026 14:00

charliermarsh requested a review from dhruvmanila as a code owner April 3, 2026 14:00

charliermarsh force-pushed the charlie/formatter-multiline branch from 2af1535 to 215c43d Compare April 3, 2026 14:00

MichaReiser approved these changes Apr 3, 2026

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charliermarsh force-pushed the charlie/parser-multiline branch 3 times, most recently from 3144fb7 to d2cd4d1 Compare April 5, 2026 15:04

Base automatically changed from charlie/parser-multiline to main April 5, 2026 15:09

Avoid emitting multi-line f-string elements before Python 3.12

a24edfe

charliermarsh force-pushed the charlie/formatter-multiline branch from 215c43d to a24edfe Compare April 5, 2026 15:10

charliermarsh enabled auto-merge (squash) April 5, 2026 15:10

charliermarsh merged commit 1fe1c5f into main Apr 5, 2026
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charliermarsh deleted the charlie/formatter-multiline branch April 5, 2026 15:14

BrewTestBot mentioned this pull request Apr 9, 2026

ruff 0.15.10 Homebrew/homebrew-core#276824

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Avoid emitting multi-line f-string elements before Python 3.12#24377

Avoid emitting multi-line f-string elements before Python 3.12#24377
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charliermarsh commented Apr 2, 2026

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charliermarsh commented Apr 2, 2026

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