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False positive f-string SyntaxError #7778

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youknowone opened this issue Oct 3, 2023 · 1 comment · Fixed by #7780
Closed

False positive f-string SyntaxError #7778

youknowone opened this issue Oct 3, 2023 · 1 comment · Fixed by #7780
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@dhruvmanila
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bug Something isn't working parser Related to the parser

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@youknowone
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# x.py
f"{1:{{1}.pop()}{f'n'}}"
$ ruff x.py
error: Failed to parse x.py:1:16: f-string: single '}' is not allowed
x.py:1:16: E999 SyntaxError: f-string: single '}' is not allowed
Found 1 error.
$ ruff --version
ruff 0.0.292
@youknowone youknowone mentioned this issue Oct 3, 2023
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@dhruvmanila
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Thanks for the bug report! It seems to be caused by the two {{ inside the format spec part. It seems that the rules for escaping {/} are different in and out of a format spec.

@dhruvmanila dhruvmanila added bug Something isn't working parser Related to the parser labels Oct 3, 2023
@dhruvmanila dhruvmanila self-assigned this Oct 3, 2023
@dhruvmanila dhruvmanila mentioned this issue Oct 3, 2023
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dhruvmanila added a commit that referenced this issue Oct 3, 2023
@dhruvmanila
Avoid curly brace escape in f-string format spec (#7780)
69b8136 
## Summary

This PR fixes a bug in the lexer for f-string format spec where it would
consider the `{{` (double curly braces) as an escape pattern.

This is not the case as evident by the
[PEP](https://peps.python.org/pep-0701/#how-to-produce-these-new-tokens)
as well but I missed the part:

> [..]
> * **If in “format specifier mode” (see step 3), an opening brace ({)
or a closing brace (}).**
> * If not in “format specifier mode” (see step 3), an opening brace ({)
or a closing brace (}) that is not immediately followed by another
opening/closing brace.

## Test Plan

Add a test case to verify the fix and update the snapshot.

fixes: #7778
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Avoid curly brace escape in f-string format spec astral-sh/ruff
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@youknowone @dhruvmanila