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[syntax-errors] Positional-only parameters before Python 3.8 (#16481)
Summary -- Detect positional-only parameters before Python 3.8, as marked by the `/` separator in a parameter list. Test Plan -- Inline tests.
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‎crates/ruff_python_parser/resources/inline/err/pos_only_py37.py

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# parse_options: {"target-version": "3.7"}
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def foo(a, /): ...
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def foo(a, /, b, /): ...
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def foo(a, *args, /, b): ...
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def foo(a, //): ...

‎crates/ruff_python_parser/resources/inline/ok/pos_only_py38.py

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# parse_options: {"target-version": "3.8"}
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def foo(a, /): ...

‎crates/ruff_python_parser/src/error.rs

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@@ -449,6 +449,32 @@ pub enum UnsupportedSyntaxErrorKind {
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Match,
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Walrus,
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ExceptStar,
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/// Represents the use of a [PEP 570] positional-only parameter before Python 3.8.
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///
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/// ## Examples
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///
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/// Python 3.8 added the `/` syntax for marking preceding parameters as positional-only:
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///
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/// ```python
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/// def foo(a, b, /, c): ...
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/// ```
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///
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/// This means `a` and `b` in this case can only be provided by position, not by name. In other
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/// words, this code results in a `TypeError` at runtime:
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///
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/// ```pycon
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/// >>> def foo(a, b, /, c): ...
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/// ...
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/// >>> foo(a=1, b=2, c=3)
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/// Traceback (most recent call last):
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/// File "<python-input-3>", line 1, in <module>
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/// foo(a=1, b=2, c=3)
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/// ~~~^^^^^^^^^^^^^^^
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/// TypeError: foo() got some positional-only arguments passed as keyword arguments: 'a, b'
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/// ```
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///
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/// [PEP 570]: https://peps.python.org/pep-0570/
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PositionalOnlyParameter,
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/// Represents the use of a [type parameter list] before Python 3.12.
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///
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/// ## Examples
@@ -487,6 +513,9 @@ impl Display for UnsupportedSyntaxError {
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UnsupportedSyntaxErrorKind::Match => "Cannot use `match` statement",
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UnsupportedSyntaxErrorKind::Walrus => "Cannot use named assignment expression (`:=`)",
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UnsupportedSyntaxErrorKind::ExceptStar => "Cannot use `except*`",
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UnsupportedSyntaxErrorKind::PositionalOnlyParameter => {
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"Cannot use positional-only parameter separator"
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}
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UnsupportedSyntaxErrorKind::TypeParameterList => "Cannot use type parameter lists",
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UnsupportedSyntaxErrorKind::TypeAliasStatement => "Cannot use `type` alias statement",
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UnsupportedSyntaxErrorKind::TypeParamDefault => {
@@ -509,6 +538,7 @@ impl UnsupportedSyntaxErrorKind {
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UnsupportedSyntaxErrorKind::Match => PythonVersion::PY310,
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UnsupportedSyntaxErrorKind::Walrus => PythonVersion::PY38,
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UnsupportedSyntaxErrorKind::ExceptStar => PythonVersion::PY311,
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UnsupportedSyntaxErrorKind::PositionalOnlyParameter => PythonVersion::PY38,
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UnsupportedSyntaxErrorKind::TypeParameterList => PythonVersion::PY312,
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UnsupportedSyntaxErrorKind::TypeAliasStatement => PythonVersion::PY312,
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UnsupportedSyntaxErrorKind::TypeParamDefault => PythonVersion::PY313,

‎crates/ruff_python_parser/src/parser/statement.rs

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@@ -3050,6 +3050,21 @@ impl<'src> Parser<'src> {
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// first time, otherwise it's a user error.
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std::mem::swap(&mut parameters.args, &mut parameters.posonlyargs);
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seen_positional_only_separator = true;
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// test_ok pos_only_py38
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// # parse_options: {"target-version": "3.8"}
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// def foo(a, /): ...
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// test_err pos_only_py37
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// # parse_options: {"target-version": "3.7"}
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// def foo(a, /): ...
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// def foo(a, /, b, /): ...
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// def foo(a, *args, /, b): ...
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// def foo(a, //): ...
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parser.add_unsupported_syntax_error(
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UnsupportedSyntaxErrorKind::PositionalOnlyParameter,
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slash_range,
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);
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}
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last_keyword_only_separator_range = None;

‎crates/ruff_python_parser/tests/snapshots/invalid_syntax@pos_only_py37.py.snap

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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/pos_only_py37.py
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---
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## AST
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```
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Module(
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ModModule {
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range: 0..136,
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body: [
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FunctionDef(
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StmtFunctionDef {
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range: 43..61,
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is_async: false,
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decorator_list: [],
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name: Identifier {
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id: Name("foo"),
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range: 47..50,
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},
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type_params: None,
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parameters: Parameters {
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range: 50..56,
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posonlyargs: [
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ParameterWithDefault {
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range: 51..52,
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parameter: Parameter {
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range: 51..52,
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name: Identifier {
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id: Name("a"),
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range: 51..52,
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},
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annotation: None,
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},
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default: None,
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},
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],
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args: [],
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vararg: None,
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kwonlyargs: [],
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kwarg: None,
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},
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returns: None,
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body: [
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Expr(
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StmtExpr {
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range: 58..61,
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value: EllipsisLiteral(
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ExprEllipsisLiteral {
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range: 58..61,
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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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FunctionDef(
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StmtFunctionDef {
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range: 62..86,
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is_async: false,
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decorator_list: [],
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name: Identifier {
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id: Name("foo"),
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range: 66..69,
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},
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type_params: None,
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parameters: Parameters {
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range: 69..81,
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posonlyargs: [
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ParameterWithDefault {
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range: 70..71,
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parameter: Parameter {
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range: 70..71,
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name: Identifier {
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id: Name("a"),
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range: 70..71,
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},
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annotation: None,
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},
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default: None,
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},
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],
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args: [
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ParameterWithDefault {
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range: 76..77,
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parameter: Parameter {
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range: 76..77,
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name: Identifier {
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id: Name("b"),
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range: 76..77,
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},
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annotation: None,
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},
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default: None,
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},
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],
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vararg: None,
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kwonlyargs: [],
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kwarg: None,
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},
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returns: None,
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body: [
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Expr(
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StmtExpr {
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range: 83..86,
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value: EllipsisLiteral(
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ExprEllipsisLiteral {
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range: 83..86,
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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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FunctionDef(
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StmtFunctionDef {
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range: 87..115,
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is_async: false,
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decorator_list: [],
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name: Identifier {
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id: Name("foo"),
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range: 91..94,
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},
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type_params: None,
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parameters: Parameters {
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range: 94..110,
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posonlyargs: [
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ParameterWithDefault {
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range: 95..96,
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parameter: Parameter {
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range: 95..96,
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name: Identifier {
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id: Name("a"),
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range: 95..96,
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},
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annotation: None,
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},
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default: None,
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},
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],
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args: [],
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vararg: Some(
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Parameter {
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range: 98..103,
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name: Identifier {
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id: Name("args"),
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range: 99..103,
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},
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annotation: None,
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},
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),
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kwonlyargs: [
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ParameterWithDefault {
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range: 108..109,
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parameter: Parameter {
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range: 108..109,
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name: Identifier {
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id: Name("b"),
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range: 108..109,
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},
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annotation: None,
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},
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default: None,
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},
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],
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kwarg: None,
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},
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returns: None,
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body: [
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Expr(
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StmtExpr {
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range: 112..115,
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value: EllipsisLiteral(
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ExprEllipsisLiteral {
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range: 112..115,
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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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FunctionDef(
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StmtFunctionDef {
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range: 116..135,
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is_async: false,
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decorator_list: [],
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name: Identifier {
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id: Name("foo"),
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range: 120..123,
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},
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type_params: None,
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parameters: Parameters {
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range: 123..130,
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posonlyargs: [],
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args: [
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ParameterWithDefault {
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range: 124..125,
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parameter: Parameter {
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range: 124..125,
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name: Identifier {
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id: Name("a"),
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range: 124..125,
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},
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annotation: None,
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},
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default: None,
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},
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],
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vararg: None,
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kwonlyargs: [],
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kwarg: None,
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},
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returns: None,
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body: [
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Expr(
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StmtExpr {
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range: 132..135,
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value: EllipsisLiteral(
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ExprEllipsisLiteral {
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range: 132..135,
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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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},
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)
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```
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## Errors
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|
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1 | # parse_options: {"target-version": "3.7"}
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2 | def foo(a, /): ...
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3 | def foo(a, /, b, /): ...
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| ^ Syntax Error: Only one '/' separator allowed
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4 | def foo(a, *args, /, b): ...
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5 | def foo(a, //): ...
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|
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|
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2 | def foo(a, /): ...
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3 | def foo(a, /, b, /): ...
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4 | def foo(a, *args, /, b): ...
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| ^ Syntax Error: '/' parameter must appear before '*' parameter
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5 | def foo(a, //): ...
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|
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|
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3 | def foo(a, /, b, /): ...
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4 | def foo(a, *args, /, b): ...
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5 | def foo(a, //): ...
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| ^^ Syntax Error: Expected ',', found '//'
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|
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## Unsupported Syntax Errors
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|
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1 | # parse_options: {"target-version": "3.7"}
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2 | def foo(a, /): ...
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| ^ Syntax Error: Cannot use positional-only parameter separator on Python 3.7 (syntax was added in Python 3.8)
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3 | def foo(a, /, b, /): ...
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4 | def foo(a, *args, /, b): ...
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|
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|
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1 | # parse_options: {"target-version": "3.7"}
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2 | def foo(a, /): ...
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3 | def foo(a, /, b, /): ...
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| ^ Syntax Error: Cannot use positional-only parameter separator on Python 3.7 (syntax was added in Python 3.8)
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4 | def foo(a, *args, /, b): ...
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5 | def foo(a, //): ...
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|
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|
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2 | def foo(a, /): ...
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3 | def foo(a, /, b, /): ...
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4 | def foo(a, *args, /, b): ...
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| ^ Syntax Error: Cannot use positional-only parameter separator on Python 3.7 (syntax was added in Python 3.8)
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5 | def foo(a, //): ...
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|

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