Made PEP 747 (Annotating Type Forms) no longer experimental by Viicos · Pull Request #11302 · microsoft/pyright

Viicos · 2026-03-02T11:41:35Z

as it was recently accepted: https://discuss.python.org/t/55984/103.

github-actions · 2026-03-02T17:53:07Z

Diff from mypy_primer, showing the effect of this PR on open source code:

bidict (https://github.com/jab/bidict)
+   .../projects/bidict/bidict/_typing.py:31:28 - error: Variable not allowed in type expression (reportInvalidTypeForm)
+   .../projects/bidict/bidict/_typing.py:31:28 - error: Type arguments for "Literal" must be None, a literal value (int, bool, str, or bytes), or an enum value (reportInvalidTypeForm)
- 12 errors, 2 warnings, 0 informations
+ 14 errors, 2 warnings, 0 informations

ibis (https://github.com/ibis-project/ibis)
+   .../projects/ibis/ibis/expr/datatypes/core.py:1062:23 - error: No parameter named "geotype" (reportCallIssue)
+   .../projects/ibis/ibis/expr/datatypes/core.py:1063:24 - error: No parameter named "geotype" (reportCallIssue)
- 7557 errors, 262 warnings, 0 informations
+ 7559 errors, 262 warnings, 0 informations

sympy (https://github.com/sympy/sympy)
+   .../projects/sympy/sympy/core/add.py:93:7 - error: Base classes for class "Add" define method "sort_key" in incompatible way
+     Return type mismatch: base method returns type "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]", override returns type "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]"
+       "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]" is not assignable to "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]"
+         Tuple entry 4 is incorrect type
+           "Number" is not assignable to "One" (reportIncompatibleMethodOverride)
-   .../projects/sympy/sympy/core/cache.py:135:8 - error: "lower" is not a known attribute of "None" (reportOptionalMemberAccess)
-   .../projects/sympy/sympy/core/cache.py:139:32 - error: Argument of type "str | Unknown | None" cannot be assigned to parameter "x" of type "ConvertibleToInt" in function "__new__"
-     Type "str | Unknown | None" is not assignable to type "ConvertibleToInt"
-       Type "None" is not assignable to type "ConvertibleToInt"
-         "None" is not assignable to "str"
-         "None" is incompatible with protocol "Buffer"
-           "__buffer__" is not present
-         "None" is incompatible with protocol "SupportsInt"
-           "__int__" is not present
-         "None" is incompatible with protocol "SupportsIndex"
-     ... (reportArgumentType)
-   .../projects/sympy/sympy/core/cache.py:139:32 - error: Argument of type "str | Unknown | None" cannot be assigned to parameter "x" of type "ConvertibleToInt" in function "__new__"
-     Type "str | Unknown | None" is not assignable to type "ConvertibleToInt"
-       Type "None" is not assignable to type "ConvertibleToInt"
-         "None" is not assignable to "str"
-         "None" is incompatible with protocol "Buffer"
-           "__buffer__" is not present
-         "None" is incompatible with protocol "SupportsInt"
-           "__int__" is not present
-         "None" is incompatible with protocol "SupportsIndex" (reportArgumentType)
+   .../projects/sympy/sympy/core/expr.py:167:9 - error: Method "sort_key" overrides class "Basic" in an incompatible manner
+     Return type mismatch: base method returns type "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]", override returns type "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]"
+       "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]" is not assignable to "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]"
+         Tuple entry 4 is incorrect type
+           "Number" is not assignable to "One" (reportIncompatibleMethodOverride)
+   .../projects/sympy/sympy/core/mul.py:95:7 - error: Base classes for class "Mul" define method "sort_key" in incompatible way
+     Return type mismatch: base method returns type "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]", override returns type "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]"
+       "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]" is not assignable to "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]"
+         Tuple entry 4 is incorrect type
+           "Number" is not assignable to "One" (reportIncompatibleMethodOverride)
- .../projects/sympy/sympy/discrete/convolutions.py
-   .../projects/sympy/sympy/discrete/convolutions.py:368:13 - error: No overloads for "__setitem__" match the provided arguments (reportCallIssue)
-   .../projects/sympy/sympy/discrete/convolutions.py:368:13 - error: Argument of type "Any | One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
-     Type "Any | One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" is not assignable to type "Zero"
-       "Expr" is not assignable to "Zero" (reportArgumentType)
-   .../projects/sympy/sympy/discrete/convolutions.py:371:9 - error: No overloads for "__setitem__" match the provided arguments (reportCallIssue)
-   .../projects/sympy/sympy/discrete/convolutions.py:371:9 - error: Argument of type "Any | One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" cannot be assigned to parameter "value" of type "Zero" in function "__setitem__"
-     Type "Any | One | NegativeOne | Zero | Integer | NaN | ComplexInfinity | Rational | Infinity | NegativeInfinity | Float | Number | Expr" is not assignable to type "Zero"
-       "Expr" is not assignable to "Zero" (reportArgumentType)
+   .../projects/sympy/sympy/functions/elementary/miscellaneous.py:380:7 - error: Base classes for class "MinMaxBase" define method "sort_key" in incompatible way
+     Return type mismatch: base method returns type "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]", override returns type "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]"
+       "tuple[tuple[int, int, str], tuple[int, tuple[tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One] | Unknown | tuple[tuple[int, int, str | Unknown], tuple[int, tuple[Unknown, ...]] | tuple[int, tuple[str]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One], ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One] | Unknown, Number]" is not assignable to "tuple[tuple[int, int, str], tuple[int, tuple[Unknown, ...]], tuple[tuple[Literal[1], Literal[0], Literal['Number']], tuple[int, tuple[()]], tuple[()], One], One]"
+         Tuple entry 4 is incorrect type

... (truncated 417 lines) ...

prefect (https://github.com/PrefectHQ/prefect)
-   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:104:31 - error: Argument of type "PrefectFuture[str]" cannot be assigned to parameter "b" of type "str" in function "submit"
-     "PrefectFuture[str]" is not assignable to "str" (reportArgumentType)
+   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:103:24 - error: Cannot access attribute "submit" for class "FunctionType"
+     Attribute "submit" is unknown (reportFunctionMemberAccess)
+   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:104:17 - error: Type of "task_c" could not be determined because it refers to itself (reportGeneralTypeIssues)
-     "str" is incompatible with protocol "Awaitable[_T_co@Awaitable]"
-       "__await__" is not present (reportGeneralTypeIssues)
-   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:110:22 - error: "str" is not awaitable
+   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:177:24 - error: Cannot access attribute "submit" for class "FunctionType"
+     Attribute "submit" is unknown (reportFunctionMemberAccess)
+   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:178:17 - error: Type of "task_c" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-dask/tests/test_task_runners.py:181:25 - error: Type of "test_flow" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:220:24 - error: Cannot access attribute "submit" for class "FunctionType"
+     Attribute "submit" is unknown (reportFunctionMemberAccess)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:221:17 - error: Type of "task_c" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:224:19 - error: Type of "test_flow" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:248:17 - error: Type of "task_c" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:252:17 - error: Type of "test_flow" could not be determined because it refers to itself (reportGeneralTypeIssues)
-   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:226:22 - error: "str" is not awaitable
-     "str" is incompatible with protocol "Awaitable[_T_co@Awaitable]"
-       "__await__" is not present (reportGeneralTypeIssues)
-   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:255:24 - error: "tuple[PrefectFuture[NoReturn], PrefectFuture[NoReturn], PrefectFuture[Unknown], PrefectFuture[Unknown]]" is not awaitable
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:255:24 - error: "tuple[PrefectFuture[NoReturn], PrefectFuture[NoReturn], PrefectFuture[Unknown], Unknown]" is not awaitable
-     "tuple[PrefectFuture[NoReturn], PrefectFuture[NoReturn], PrefectFuture[Unknown], PrefectFuture[Unknown]]" is incompatible with protocol "Awaitable[_T_co@Awaitable]"
+     "tuple[PrefectFuture[NoReturn], PrefectFuture[NoReturn], PrefectFuture[Unknown], Unknown]" is incompatible with protocol "Awaitable[_T_co@Awaitable]"
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:294:24 - error: Cannot access attribute "submit" for class "FunctionType"
+     Attribute "submit" is unknown (reportFunctionMemberAccess)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:295:17 - error: Type of "task_c" could not be determined because it refers to itself (reportGeneralTypeIssues)
+   .../projects/prefect/src/integrations/prefect-ray/tests/test_task_runners.py:298:25 - error: Type of "test_flow" could not be determined because it refers to itself (reportGeneralTypeIssues)
- 5978 errors, 179 warnings, 0 informations
+ 5988 errors, 179 warnings, 0 informations

pip (https://github.com/pypa/pip)
+ .../projects/pip/src/pip/_vendor/rich/table.py
+   .../projects/pip/src/pip/_vendor/rich/table.py:939:13 - error: No parameter named "caption_justify" (reportCallIssue)
- 1107 errors, 31 warnings, 0 informations
+ 1108 errors, 31 warnings, 0 informations

static-frame (https://github.com/static-frame/static-frame)
+   .../projects/static-frame/static_frame/core/util.py:1044:32 - error: Attribute type cannot use type variable "TVFGItem@__init__" scoped to local method (reportGeneralTypeIssues)
- 58 errors, 71 warnings, 0 informations
+ 59 errors, 71 warnings, 0 informations

rich (https://github.com/Textualize/rich)
+ .../projects/rich/rich/table.py
+   .../projects/rich/rich/table.py:948:13 - error: No parameter named "caption_justify" (reportCallIssue)
- 369 errors, 43 warnings, 0 informations
+ 370 errors, 43 warnings, 0 informations

rchiodo · 2026-03-02T18:22:54Z

@Viicos, it looks like the changes are causing a single test failure.

Viicos · 2026-03-02T20:15:51Z

Looks like a bug, that can be reproduce with the following MRE:

from typing import NamedTuple

# X is necessary to reproduce. Doesn't reproduce with only "a" as a field
X = NamedTuple("X", [("a", int), ("b", str)])
X(1, "1")


class Z(NamedTuple):
    c: list[str]
    d: list[int]


q6 = Z(["1"], [3])  # Error: Class definition for "Z" depends on itself

# This is necessary to reproduce
for a, b in zip(*q6):  # needs to be named a and b to reproduce
    pass

LLM analysis

The isTypeFormSupported guard on getTypeOfStringList (line 1715) was the critical one. By removing it, the commit causes every string literal to be
speculatively evaluated as a type expression to extract TypeForm info.

The chain of events:

X = NamedTuple("X", [("a", int), ("b", str)]) is being processed
The string "a" is now speculatively parsed as a type expression (line 1739: getTypeOfStringListAsType)
"a" is parsed as the identifier a, which resolves to the for-loop variable a from for a, b in zip(*q6):
To infer a's type, pyright evaluates the for-loop expression zip(*q6) 5. This requires q6's type → code flow follows to q6 = Z(["1"], [3]) 6. Evaluating Z(["1"], [3]) triggers Z's class evaluation → Z is marked PartiallyEvaluated
validateConstructorArgs calls validateMetaclassCall first (constructors.ts:132), which calls getBoundCallMethod → getTypeOfBoundMember(Z,
"call")
Z is still PartiallyEvaluated → cycle error

The reason both X and the zip call are needed:

X is needed because its "a" string literal is what triggers the speculative type evaluation
*zip(q6) is needed because the for-loop variable a is what the identifier a resolves to, and evaluating that loop requires Z's constructor

The fix should restore the isTypeFormSupported guard specifically for the string-as-TypeForm path, or find a way to avoid the speculative type
evaluation causing this cascade.

Made PEP 747 (Annotating Type Forms) no longer experimental

f6016a2

rchiodo approved these changes Mar 2, 2026

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Made PEP 747 (Annotating Type Forms) no longer experimental#11302

Made PEP 747 (Annotating Type Forms) no longer experimental#11302
Viicos wants to merge 1 commit intomicrosoft:mainfrom
Viicos:pep-747-no-exp

Viicos commented Mar 2, 2026

Uh oh!

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rchiodo commented Mar 2, 2026

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Viicos commented Mar 2, 2026 •

edited

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Viicos commented Mar 2, 2026

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rchiodo commented Mar 2, 2026

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Viicos commented Mar 2, 2026 •

edited

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