[ty] Forbid use of `super()` in `NamedTuple` subclasses #21700

charliermarsh · 2025-11-30T03:02:11Z

Summary

The exact behavior around what's allowed vs. disallowed was partly detected through trial and error in the runtime.

I was a little confused by this comment that says "NamedTuple subclasses cannot be inherited from" because in practice that doesn't appear to error at runtime.

Closes #1683.

astral-sh-bot · 2025-11-30T03:04:46Z

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

astral-sh-bot · 2025-11-30T03:06:42Z

`mypy_primer` results

Changes were detected when running on open source projects

scikit-build-core (https://github.com/scikit-build/scikit-build-core)
+ src/scikit_build_core/build/_pathutil.py:25:38: error[invalid-argument-type] Argument to function `__new__` is incorrect: Expected `str | PathLike[str]`, found `DirEntry[Path]`
+ src/scikit_build_core/build/_pathutil.py:27:24: error[invalid-argument-type] Argument to function `__new__` is incorrect: Expected `str | PathLike[str]`, found `DirEntry[Path]`
+ src/scikit_build_core/build/wheel.py:98:20: error[no-matching-overload] No overload of bound method `__init__` matches arguments
- Found 41 diagnostics
+ Found 44 diagnostics

pydantic (https://github.com/pydantic/pydantic)
- pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
+ pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
- pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, Divergent], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`
+ pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`

No memory usage changes detected ✅

AlexWaygood

Thank you, this is excellent! Just a few nitpicks really

AlexWaygood · 2025-11-30T12:41:05Z

crates/ty_python_semantic/resources/mdtest/named_tuple.md

+
+## `super()` is not supported in NamedTuple methods
+
+Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime. In Python


extremely nitpicky comment: my preferred term is "NamedTuple class" rather than "NamedTuple subclass". The generated class doesn't actually have NamedTuple in its MRO (because NamedTuple is actually a function rather than a class!) -- the generated class actually inherits directly from tuple. The runtime does some magic to swap out NamedTuple for tuple in the class's bases, so it feels slightly incorrect to refer to it as a "subclass of" NamedTuple, even if NamedTuple is included in the class's bases.

Suggested change

Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime. In Python

Using `super()` in a method of a `NamedTuple` class will raise an exception at runtime. In Python

AlexWaygood · 2025-11-30T12:42:06Z

crates/ty_python_semantic/resources/mdtest/named_tuple.md

You could also add a test to verify that using super() on a NamedTuple class works fine if it occurs outside the class, e.g.

class F(NamedTuple): x: int super(F, F(42)) # fine

AlexWaygood · 2025-11-30T12:43:37Z

crates/ty_python_semantic/src/types/class.rs

+                                .report_lint(&SUPER_CALL_IN_NAMED_TUPLE_METHOD, call_expression)
+                            {
+                                builder.into_diagnostic(format_args!(
+                                    "Cannot use `super()` in a method of NamedTuple subclass `{}`",


Suggested change

"Cannot use `super()` in a method of NamedTuple subclass `{}`",

"Cannot use `super()` in a method of NamedTuple class `{}`",

AlexWaygood · 2025-11-30T12:43:45Z

crates/ty_python_semantic/src/types/class.rs

+                                    .report_lint(&SUPER_CALL_IN_NAMED_TUPLE_METHOD, call_expression)
+                                {
+                                    builder.into_diagnostic(format_args!(
+                                        "Cannot use `super()` in a method of NamedTuple subclass `{}`",


Suggested change

"Cannot use `super()` in a method of NamedTuple subclass `{}`",

"Cannot use `super()` in a method of NamedTuple class `{}`",

AlexWaygood · 2025-11-30T12:43:52Z

crates/ty_python_semantic/src/types/diagnostic.rs


+declare_lint! {
+    /// ## What it does
+    /// Checks for calls to `super()` inside methods of `NamedTuple` subclasses.


Suggested change

/// Checks for calls to `super()` inside methods of `NamedTuple` subclasses.

/// Checks for calls to `super()` inside methods of `NamedTuple` classes.

AlexWaygood · 2025-11-30T12:44:01Z

crates/ty_python_semantic/src/types/diagnostic.rs

+    /// Checks for calls to `super()` inside methods of `NamedTuple` subclasses.
+    ///
+    /// ## Why is this bad?
+    /// Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime.


Suggested change

/// Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime.

/// Using `super()` in a method of a `NamedTuple` class will raise an exception at runtime.

AlexWaygood · 2025-11-30T12:45:05Z

crates/ty_python_semantic/src/types/diagnostic.rs

+        summary: "detects `super()` calls in methods of `NamedTuple` subclasses",
+        status: LintStatus::preview("1.0.0"),


Suggested change

summary: "detects `super()` calls in methods of `NamedTuple` subclasses",

status: LintStatus::preview("1.0.0"),

summary: "detects `super()` calls in methods of `NamedTuple` classes",

status: LintStatus::preview("0.0.1-alpha.30"),

AlexWaygood · 2025-11-30T12:49:23Z

I was a little confused by this comment that says "NamedTuple subclasses cannot be inherited from" because in practice that doesn't appear to error at runtime.

yeah, I think that comment was just incorrect

codspeed-hq · 2025-11-30T16:03:05Z

CodSpeed Performance Report

Merging #21700 will improve performances by 4.45%

_{Comparing charlie/named (664df36) with main (b02e821)}

Summary

⚡ 1 improvement
✅ 21 untouched
⏩ 30 skipped¹

Benchmarks breakdown

	Mode	Benchmark	`BASE`	`HEAD`	Change
⚡	WallTime	`large[pydantic]`	207.5 s	198.7 s	+4.45%

30 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

charliermarsh requested review from AlexWaygood, carljm, dcreager and sharkdp as code owners November 30, 2025 03:02

charliermarsh force-pushed the charlie/named branch from 42b3fb3 to 05bcf6b Compare November 30, 2025 03:02

charliermarsh added the ty Multi-file analysis & type inference label Nov 30, 2025

charliermarsh changed the title ~~Forbid use of super() in NamedTuple subclasses~~ [ty] Forbid use of super() in NamedTuple subclasses Nov 30, 2025

charliermarsh force-pushed the charlie/named branch 2 times, most recently from ca3d7ae to 25b9574 Compare November 30, 2025 03:13

charliermarsh requested a review from MichaReiser as a code owner November 30, 2025 03:13

AlexWaygood approved these changes Nov 30, 2025

View reviewed changes

charliermarsh enabled auto-merge (squash) November 30, 2025 15:34

charliermarsh added 2 commits November 30, 2025 10:43

Forbid use of super in NamedTuple subclasses

c042e73

Review feedback

664df36

charliermarsh force-pushed the charlie/named branch from aa3249c to 664df36 Compare November 30, 2025 15:44

charliermarsh merged commit e7beb7e into main Nov 30, 2025
40 checks passed

charliermarsh deleted the charlie/named branch November 30, 2025 15:49


		## `super()` is not supported in NamedTuple methods

		Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime. In Python

	"Cannot use `super()` in a method of NamedTuple subclass `{}`",
	"Cannot use `super()` in a method of NamedTuple class `{}`",

	/// Checks for calls to `super()` inside methods of `NamedTuple` subclasses.
	/// Checks for calls to `super()` inside methods of `NamedTuple` classes.

	/// Using `super()` in a method of a `NamedTuple` subclass will raise an exception at runtime.
	/// Using `super()` in a method of a `NamedTuple` class will raise an exception at runtime.

		summary: "detects `super()` calls in methods of `NamedTuple` subclasses",
		status: LintStatus::preview("1.0.0"),

[ty] Forbid use of super() in NamedTuple subclasses #21700

[ty] Forbid use of super() in NamedTuple subclasses #21700

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AlexWaygood commented Nov 30, 2025

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codspeed-hq bot commented Nov 30, 2025

Merging #21700 will improve performances by 4.45%

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[ty] Forbid use of `super()` in `NamedTuple` subclasses #21700

[ty] Forbid use of `super()` in `NamedTuple` subclasses #21700

charliermarsh commented Nov 30, 2025 •

edited by MichaReiser

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`mypy_primer` results