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ntBrentBre
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[syntax-errors] Single starred assignment target (#17024)
Summary -- Detects starred assignment targets outside of tuples and lists like `*a = (1,)`. This PR only considers assignment statements. I also checked annotated assigment statements, but these give a separate error that we already catch, so I think they're okay not to consider: ```pycon >>> *a: list[int] = [] File "<python-input-72>", line 1 *a: list[int] = [] ^ SyntaxError: invalid syntax ``` Fixes #13759 Test Plan -- New inline tests, plus a new `SemanticSyntaxError` for an existing parser test. I also removed a now-invalid case from an otherwise-valid test fixture. The new semantic error leads to two errors for the case below: ```python *foo() = 42 ``` but this matches [pyright] too. [pyright]: https://pyright-play.net/?code=FQMw9mAUCUAEC8sAsAmAUEA
1 parent a0819f0 commit ab1011c

9 files changed

+343
-116
lines changed

‎crates/ruff_linter/src/checkers/ast/mod.rs

+5-9
Original file line numberDiff line numberDiff line change
@@ -551,16 +551,12 @@ impl SemanticSyntaxContext for Checker<'_> {
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| SemanticSyntaxErrorKind::DuplicateTypeParameter
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| SemanticSyntaxErrorKind::MultipleCaseAssignment(_)
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| SemanticSyntaxErrorKind::IrrefutableCasePattern(_)
554-
| SemanticSyntaxErrorKind::WriteToDebug(_)
555-
if self.settings.preview.is_enabled() =>
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{
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self.semantic_errors.borrow_mut().push(error);
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| SemanticSyntaxErrorKind::SingleStarredAssignment
555+
| SemanticSyntaxErrorKind::WriteToDebug(_) => {
556+
if self.settings.preview.is_enabled() {
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self.semantic_errors.borrow_mut().push(error);
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}
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}
559-
SemanticSyntaxErrorKind::ReboundComprehensionVariable
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| SemanticSyntaxErrorKind::DuplicateTypeParameter
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| SemanticSyntaxErrorKind::MultipleCaseAssignment(_)
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| SemanticSyntaxErrorKind::IrrefutableCasePattern(_)
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| SemanticSyntaxErrorKind::WriteToDebug(_) => {}
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}
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}
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}

‎crates/ruff_python_parser/resources/inline/err/single_starred_assignment_target.py

+1
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
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*a = (1,)

‎crates/ruff_python_parser/resources/inline/ok/single_starred_assignment_target.py

+3
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,3 @@
1+
(*a,) = (1,)
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*a, = (1,)
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[*a] = (1,)

‎crates/ruff_python_parser/resources/valid/statement/assignment.py

-2
Original file line numberDiff line numberDiff line change
@@ -14,8 +14,6 @@
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# This last group of tests checks that assignments we expect to be parsed
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# (including some interesting ones) continue to be parsed successfully.
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17-
*foo = 42
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[x, y, z] = [1, 2, 3]
2018

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(x, y, z) = (1, 2, 3)

‎crates/ruff_python_parser/src/semantic_errors.rs

+36
Original file line numberDiff line numberDiff line change
@@ -73,6 +73,22 @@ impl SemanticSyntaxChecker {
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Self::duplicate_type_parameter_name(type_params, ctx);
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}
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}
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Stmt::Assign(ast::StmtAssign { targets, .. }) => {
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if let [Expr::Starred(ast::ExprStarred { range, .. })] = targets.as_slice() {
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// test_ok single_starred_assignment_target
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// (*a,) = (1,)
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// *a, = (1,)
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// [*a] = (1,)
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// test_err single_starred_assignment_target
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// *a = (1,)
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Self::add_error(
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ctx,
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SemanticSyntaxErrorKind::SingleStarredAssignment,
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*range,
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);
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}
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}
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_ => {}
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}
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@@ -437,6 +453,9 @@ impl Display for SemanticSyntaxError {
437453
f.write_str("wildcard makes remaining patterns unreachable")
438454
}
439455
},
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SemanticSyntaxErrorKind::SingleStarredAssignment => {
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f.write_str("starred assignment target must be in a list or tuple")
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}
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SemanticSyntaxErrorKind::WriteToDebug(kind) => match kind {
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WriteToDebugKind::Store => f.write_str("cannot assign to `__debug__`"),
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WriteToDebugKind::Delete(python_version) => {
@@ -522,6 +541,23 @@ pub enum SemanticSyntaxErrorKind {
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/// [Python reference]: https://docs.python.org/3/reference/compound_stmts.html#irrefutable-case-blocks
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IrrefutableCasePattern(IrrefutablePatternKind),
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544+
/// Represents a single starred assignment target outside of a tuple or list.
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///
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/// ## Examples
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///
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/// ```python
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/// *a = (1,) # SyntaxError
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/// ```
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///
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/// A starred assignment target can only occur within a tuple or list:
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///
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/// ```python
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/// b, *a = 1, 2, 3
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/// (*a,) = 1, 2, 3
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/// [*a] = 1, 2, 3
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/// ```
559+
SingleStarredAssignment,
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525561
/// Represents a write to `__debug__`. This includes simple assignments and deletions as well
526562
/// other kinds of statements that can introduce bindings, such as type parameters in functions,
527563
/// classes, and aliases, `match` arms, and imports, among others.

‎crates/ruff_python_parser/tests/snapshots/invalid_syntax@single_starred_assignment_target.py.snap

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@@ -0,0 +1,58 @@
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---
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source: crates/ruff_python_parser/tests/fixtures.rs
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input_file: crates/ruff_python_parser/resources/inline/err/single_starred_assignment_target.py
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---
5+
## AST
6+
7+
```
8+
Module(
9+
ModModule {
10+
range: 0..10,
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body: [
12+
Assign(
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StmtAssign {
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range: 0..9,
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targets: [
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Starred(
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ExprStarred {
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range: 0..2,
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value: Name(
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ExprName {
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range: 1..2,
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id: Name("a"),
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ctx: Store,
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},
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),
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ctx: Store,
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},
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),
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],
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value: Tuple(
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ExprTuple {
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range: 5..9,
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elts: [
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NumberLiteral(
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ExprNumberLiteral {
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range: 6..7,
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value: Int(
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1,
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),
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},
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),
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],
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ctx: Load,
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parenthesized: true,
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},
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),
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},
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),
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],
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},
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)
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```
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## Semantic Syntax Errors
54+
55+
|
56+
1 | *a = (1,)
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| ^^ Syntax Error: starred assignment target must be in a list or tuple
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|

‎crates/ruff_python_parser/tests/snapshots/invalid_syntax@statements__invalid_assignment_targets.py.snap

+12
Original file line numberDiff line numberDiff line change
@@ -1690,3 +1690,15 @@ Module(
16901690
42 | (x, foo(), y) = (42, 42, 42)
16911691
| ^^^^^ Syntax Error: Invalid assignment target
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|
1693+
1694+
1695+
## Semantic Syntax Errors
1696+
1697+
|
1698+
37 | None = 42
1699+
38 | ... = 42
1700+
39 | *foo() = 42
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| ^^^^^^ Syntax Error: starred assignment target must be in a list or tuple
1702+
40 | [x, foo(), y] = [42, 42, 42]
1703+
41 | [[a, b], [[42]], d] = [[1, 2], [[3]], 4]
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|

‎crates/ruff_python_parser/tests/snapshots/valid_syntax@single_starred_assignment_target.py.snap

+152
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,152 @@
1+
---
2+
source: crates/ruff_python_parser/tests/fixtures.rs
3+
input_file: crates/ruff_python_parser/resources/inline/ok/single_starred_assignment_target.py
4+
---
5+
## AST
6+
7+
```
8+
Module(
9+
ModModule {
10+
range: 0..36,
11+
body: [
12+
Assign(
13+
StmtAssign {
14+
range: 0..12,
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targets: [
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Tuple(
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ExprTuple {
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range: 0..5,
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elts: [
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Starred(
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ExprStarred {
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range: 1..3,
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value: Name(
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ExprName {
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range: 2..3,
26+
id: Name("a"),
27+
ctx: Store,
28+
},
29+
),
30+
ctx: Store,
31+
},
32+
),
33+
],
34+
ctx: Store,
35+
parenthesized: true,
36+
},
37+
),
38+
],
39+
value: Tuple(
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ExprTuple {
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range: 8..12,
42+
elts: [
43+
NumberLiteral(
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ExprNumberLiteral {
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range: 9..10,
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value: Int(
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1,
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),
49+
},
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),
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],
52+
ctx: Load,
53+
parenthesized: true,
54+
},
55+
),
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},
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),
58+
Assign(
59+
StmtAssign {
60+
range: 13..23,
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targets: [
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Tuple(
63+
ExprTuple {
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range: 13..16,
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elts: [
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Starred(
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ExprStarred {
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range: 13..15,
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value: Name(
70+
ExprName {
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range: 14..15,
72+
id: Name("a"),
73+
ctx: Store,
74+
},
75+
),
76+
ctx: Store,
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},
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),
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],
80+
ctx: Store,
81+
parenthesized: false,
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},
83+
),
84+
],
85+
value: Tuple(
86+
ExprTuple {
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range: 19..23,
88+
elts: [
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NumberLiteral(
90+
ExprNumberLiteral {
91+
range: 20..21,
92+
value: Int(
93+
1,
94+
),
95+
},
96+
),
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],
98+
ctx: Load,
99+
parenthesized: true,
100+
},
101+
),
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},
103+
),
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Assign(
105+
StmtAssign {
106+
range: 24..35,
107+
targets: [
108+
List(
109+
ExprList {
110+
range: 24..28,
111+
elts: [
112+
Starred(
113+
ExprStarred {
114+
range: 25..27,
115+
value: Name(
116+
ExprName {
117+
range: 26..27,
118+
id: Name("a"),
119+
ctx: Store,
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},
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),
122+
ctx: Store,
123+
},
124+
),
125+
],
126+
ctx: Store,
127+
},
128+
),
129+
],
130+
value: Tuple(
131+
ExprTuple {
132+
range: 31..35,
133+
elts: [
134+
NumberLiteral(
135+
ExprNumberLiteral {
136+
range: 32..33,
137+
value: Int(
138+
1,
139+
),
140+
},
141+
),
142+
],
143+
ctx: Load,
144+
parenthesized: true,
145+
},
146+
),
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},
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),
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],
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},
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)
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```

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