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Remove parentheses around multiple exception types on Python 3.14+ (#20768)

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Summary
--

This PR implements the black preview style from
https://github.com/psf/black/pull/4720. As of Python 3.14, you're
allowed to omit the parentheses around groups of exceptions, as long as
there's no `as` binding:

**3.13**

```pycon
Python 3.13.4 (main, Jun  4 2025, 17:37:06) [Clang 20.1.4 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> try: ...
... except (Exception, BaseException): ...
...
Ellipsis
>>> try: ...
... except Exception, BaseException: ...
...
  File "<python-input-1>", line 2
    except Exception, BaseException: ...
           ^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: multiple exception types must be parenthesized
```

**3.14**

```pycon
Python 3.14.0rc2 (main, Sep  2 2025, 14:20:56) [Clang 20.1.4 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> try: ...
... except Exception, BaseException: ...
...
Ellipsis
>>> try: ...
... except (Exception, BaseException): ...
...
Ellipsis
>>> try: ...
... except Exception, BaseException as e: ...
...
  File "<python-input-2>", line 2
    except Exception, BaseException as e: ...
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: multiple exception types must be parenthesized when using 'as'
```

I think this ended up being pretty straightforward, at least once Micha
showed me where to start :)

Test Plan
--

New tests

At first I thought we were deviating from black in how we handle
comments within the exception type tuple, but I think this applies to
how we format all tuples, not specifically with the new preview style.
This commit is contained in:
Brent Westbrook
2025-10-14 11:17:45 -04:00
committed by GitHub
parent 1ed9b215b9
commit 591e9bbccb
8 changed files with 497 additions and 450 deletions
Download Patch File Download Diff File Expand all files Collapse all files

61
crates/ruff_python_formatter/src/other/except_handler_except_handler.rs
View File

@@ -1,10 +1,12 @@
use ruff_formatter::FormatRuleWithOptions;
use ruff_formatter::write;
use ruff_python_ast::ExceptHandlerExceptHandler;
use ruff_python_ast::{ExceptHandlerExceptHandler, Expr, PythonVersion};
use crate::expression::expr_tuple::TupleParentheses;
use crate::expression::maybe_parenthesize_expression;
use crate::expression::parentheses::Parenthesize;
use crate::prelude::*;
use crate::preview::is_remove_parens_around_except_types_enabled;
use crate::statement::clause::{ClauseHeader, clause_body, clause_header};
use crate::statement::suite::SuiteKind;
@@ -57,7 +59,7 @@ impl FormatNodeRule<ExceptHandlerExceptHandler> for FormatExceptHandlerExceptHan
clause_header(
ClauseHeader::ExceptHandler(item),
dangling_comments,
&format_with(|f| {
&format_with(|f: &mut PyFormatter| {
write!(
f,
[
@@ -69,21 +71,50 @@ impl FormatNodeRule<ExceptHandlerExceptHandler> for FormatExceptHandlerExceptHan
]
)?;
if let Some(type_) = type_ {
write!(
f,
[
space(),
maybe_parenthesize_expression(
type_,
item,
Parenthesize::IfBreaks
match type_.as_deref() {
// For tuples of exception types without an `as` name and on 3.14+, the
// parentheses are optional.
//
// ```py
// try:
// ...
// except BaseException, Exception: # Ok
// ...
// ```
Some(Expr::Tuple(tuple))
if f.options().target_version() >= PythonVersion::PY314
&& is_remove_parens_around_except_types_enabled(
f.context(),
)
]
)?;
if let Some(name) = name {
write!(f, [space(), token("as"), space(), name.format()])?;
&& name.is_none() =>
{
write!(
f,
[
space(),
tuple
.format()
.with_options(TupleParentheses::NeverPreserve)
]
)?;
}
Some(type_) => {
write!(
f,
[
space(),
maybe_parenthesize_expression(
type_,
item,
Parenthesize::IfBreaks
)
]
)?;
if let Some(name) = name {
write!(f, [space(), token("as"), space(), name.format()])?;
}
}
_ => {}
}
Ok(())