Do not iterate via __getitem__ when __iter__ is explicitly set - #11645
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Rich Chiodo (rchiodo) merged 1 commit intoAug 24, 2026
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CPython raises TypeError when __iter__ is None even if __getitem__ exists; the legacy sequence protocol applies only when __iter__ is missing.
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Diff from mypy_primer, showing the effect of this PR on open source code: sympy (https://github.com/sympy/sympy)
- .../projects/sympy/sympy/solvers/diophantine/diophantine.py:1460:50 - error: Cannot access attribute "as_coeff_Mul" for class "Basic*"
- Attribute "as_coeff_Mul" is unknown (reportAttributeAccessIssue)
- .../projects/sympy/sympy/solvers/diophantine/diophantine.py:1460:50 - error: Cannot access attribute "as_coeff_Mul" for class "Relational*"
- Attribute "as_coeff_Mul" is unknown (reportAttributeAccessIssue)
- .../projects/sympy/sympy/solvers/ode/lie_group.py:619:61 - error: Operator "-" not supported for type "Unknown | Basic" (reportOperatorIssue)
- .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:225:45 - error: Cannot access attribute "has" for class "tuple[Expr, int]"
- Attribute "has" is unknown (reportAttributeAccessIssue)
+ .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:223:22 - error: No overloads for "__new__" match the provided arguments (reportCallIssue)
+ .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:223:25 - error: Argument of type "Unknown | One | NegativeOne | Zero | Integer | tuple[Expr, int]" cannot be assigned to parameter "arg" of type "Expr" in function "__new__"
+ Type "Unknown | One | NegativeOne | Zero | Integer | tuple[Expr, int]" is not assignable to type "Expr"
+ "tuple[Expr, int]" is not assignable to "Expr" (reportArgumentType)
+ .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:238:40 - error: No overloads for "__new__" match the provided arguments (reportCallIssue)
+ .../projects/sympy/sympy/solvers/ode/nonhomogeneous.py:238:50 - error: Argument of type "Unknown | One | NegativeOne | Zero | Integer | tuple[Expr, int]" cannot be assigned to parameter "arg" of type "Expr" in function "__new__"
+ Type "Unknown | One | NegativeOne | Zero | Integer | tuple[Expr, int]" is not assignable to type "Expr"
+ "tuple[Expr, int]" is not assignable to "Expr" (reportArgumentType)
- .../projects/sympy/sympy/solvers/ode/ode.py:1433:17 - error: Argument of type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
+ .../projects/sympy/sympy/solvers/ode/ode.py:1433:17 - error: Argument of type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
- Type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" is not assignable to type "Zero"
+ Type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr" is not assignable to type "Zero"
- .../projects/sympy/sympy/solvers/ode/ode.py:2961:17 - error: Argument of type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
+ .../projects/sympy/sympy/solvers/ode/ode.py:2961:17 - error: Argument of type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
- Type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" is not assignable to type "Zero"
+ Type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr" is not assignable to type "Zero"
+ .../projects/sympy/sympy/solvers/ode/riccati.py:275:12 - error: No overloads for "__init__" match the provided arguments (reportCallIssue)
+ .../projects/sympy/sympy/solvers/ode/riccati.py:275:17 - error: Argument of type "zip[Unknown]" cannot be assigned to parameter "iterable" of type "Iterable[list[bytes]]" in function "__init__"
+ "zip[Unknown]" is incompatible with protocol "Iterable[list[bytes]]"
+ "__iter__" is an incompatible type
+ Type "() -> zip[Unknown]" is not assignable to type "() -> Iterator[_T_co@Iterable]"
+ Function return type "zip[Unknown]" is incompatible with type "Iterator[_T_co@Iterable]"
+ "zip[Unknown]" is incompatible with protocol "Iterator[_T_co@Iterable]" (reportArgumentType)
- .../projects/sympy/sympy/solvers/ode/riccati.py:874:51 - error: Cannot access attribute "diff" for class "Basic*"
- Attribute "diff" is unknown (reportAttributeAccessIssue)
+ .../projects/sympy/sympy/solvers/ode/single.py:867:9 - error: Expression with type "tuple[ComplexInfinity | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown]] | tuple[ComplexInfinity | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown], list[tuple[Unknown, Unknown]] | list[Unknown]]" cannot be assigned to target tuple
+ Type "tuple[ComplexInfinity | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown], list[tuple[Unknown, Unknown]] | list[Unknown]]" is incompatible with target tuple
+ Tuple size mismatch; expected 2 but received 3 (reportAssignmentType)
- .../projects/sympy/sympy/solvers/ode/single.py:2646:27 - error: Argument of type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr | Unknown | int" cannot be assigned to parameter "stop" of type "SupportsIndex" in function "__new__"
+ .../projects/sympy/sympy/solvers/ode/single.py:2646:27 - error: Argument of type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr | NaN | NegativeInfinity | int" cannot be assigned to parameter "stop" of type "SupportsIndex" in function "__new__"
- Type "One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr | Unknown | int" is not assignable to type "SupportsIndex"
+ Type "One | NegativeOne | Zero | Integer | Unknown | Rational | Number | Expr | NaN | NegativeInfinity | int" is not assignable to type "SupportsIndex"
- .../projects/sympy/sympy/solvers/ode/subscheck.py:270:32 - error: Operator "-" not supported for types "Basic | Unknown | Zero | Self@Basic" and "Basic | Unknown | Zero | Self@Basic"
+ .../projects/sympy/sympy/solvers/ode/subscheck.py:270:32 - error: Operator "-" not supported for types "Basic | Unknown | Zero" and "Basic | Unknown | Zero"
- Operator "-" not supported for types "Basic" and "Basic"
- Operator "-" not supported for types "Basic" and "Basic*"
- Operator "-" not supported for types "Basic*" and "Basic"
- Operator "-" not supported for types "Basic*" and "Basic*" (reportOperatorIssue)
+ Operator "-" not supported for types "Basic" and "Basic" (reportOperatorIssue)
- .../projects/sympy/sympy/solvers/ode/systems.py:1167:37 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1167:37 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "Literal[2]" and "Basic*"
- .../projects/sympy/sympy/solvers/ode/systems.py:1167:37 - error: Operator "*" not supported for types "Unknown | int | Expr" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1167:37 - error: Operator "*" not supported for types "Unknown | Expr | int" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "int" and "Basic*"
- Operator "*" not supported for types "int" and "Basic"
- Operator "*" not supported for types "Expr" and "Basic*"
+ Operator "*" not supported for types "Expr" and "Basic"
- Operator "*" not supported for types "Expr" and "Basic" (reportOperatorIssue)
+ Operator "*" not supported for types "int" and "Basic" (reportOperatorIssue)
- .../projects/sympy/sympy/solvers/ode/systems.py:1169:30 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1169:30 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "Literal[2]" and "Basic*"
- .../projects/sympy/sympy/solvers/ode/systems.py:1169:30 - error: Operator "*" not supported for types "Unknown | int | Expr" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1169:30 - error: Operator "*" not supported for types "Unknown | Expr | int" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "int" and "Basic*"
- Operator "*" not supported for types "int" and "Basic"
- Operator "*" not supported for types "Expr" and "Basic*"
+ Operator "*" not supported for types "Expr" and "Basic"
+ Operator "*" not supported for types "int" and "Basic" (reportOperatorIssue)
- .../projects/sympy/sympy/solvers/ode/systems.py:1169:49 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1169:49 - error: Operator "*" not supported for types "Literal[2]" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "Literal[2]" and "Basic*"
- .../projects/sympy/sympy/solvers/ode/systems.py:1169:49 - error: Operator "*" not supported for types "Unknown | int | Expr" and "Unknown | Self@Basic | bool | Expr | Basic"
+ .../projects/sympy/sympy/solvers/ode/systems.py:1169:49 - error: Operator "*" not supported for types "Unknown | Expr | int" and "Unknown | Expr | Basic | bool"
- Operator "*" not supported for types "int" and "Basic*"
- Operator "*" not supported for types "int" and "Basic"
- Operator "*" not supported for types "Expr" and "Basic*"
+ Operator "*" not supported for types "Expr" and "Basic"
... (truncated 1777 lines) ...
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Verification: The relevant tests could not be fully run in the isolated environment; this review is not fully verified. |
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Summary
__iter__ = Noneand__getitem__should not be iterable. #11220.__iter__is present but not callable (__iter__ = None), even if__getitem__exists. Pyright still used the legacy sequence protocol and acceptedfor x in Foo().__getitem__fallback now applies only when__iter__is missing.Test plan
npx jest typeEvaluator3.test.ts -t ForLoop --forceExit(frompackages/pyright-internal)for _ in Foo()with__iter__ = NoneraisesTypeError; a__getitem__-only class still iteratesforloop over such a class reports a not-iterable error in the language server