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Merged
JelleZijlstra merged 3 commits into from
Feb 19, 2023
Merged

Improve the first overload of is_dataclass#9758

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ac60a52
Improve the first overload of `is_dataclass`
AlexWaygood Feb 19, 2023
76c9ade
https://github.com/microsoft/pyright/issues/4339 strikes again
AlexWaygood Feb 19, 2023
7c6ca1e
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AlexWaygood Feb 19, 2023
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2 changes: 1 addition & 1 deletion stdlib/dataclasses.pyi
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Original file line numberDiff line numberDiff line change
Expand Up@@ -223,7 +223,7 @@ else:

def fields(class_or_instance: DataclassInstance | type[DataclassInstance]) -> tuple[Field[Any], ...]: ...
@overload
def is_dataclass(obj: DataclassInstance | type[DataclassInstance]) -> Literal[True]: ...
def is_dataclass(obj: DataclassInstance) -> Literal[True]: ...
@overload
def is_dataclass(obj: type) -> TypeGuard[type[DataclassInstance]]: ...
@overload
Expand Down
33 changes: 21 additions & 12 deletions test_cases/stdlib/check_dataclasses.py
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Original file line numberDiff line numberDiff line change
@@ -1,9 +1,12 @@
from __future__ import annotations

import dataclasses as dc
from typing import Any, Dict, Tuple, Type
from typing import TYPE_CHECKING, Any, Dict, Tuple, Type, Union
from typing_extensions import assert_type

if TYPE_CHECKING:
from _typeshed import DataclassInstance


@dc.dataclass
class Foo:
Expand All@@ -21,10 +24,9 @@ class Foo:
# dc.astuple(Foo)
# dc.replace(Foo)

if dc.is_dataclass(Foo):
# The inferred type doesn't change
# if it's already known to be a subtype of type[_DataclassInstance]
assert_type(Foo, Type[Foo])
# See #9723 for why we can't make this assertion
# if dc.is_dataclass(Foo):
# assert_type(Foo, Type[Foo])

f = Foo(attr="attr")

Expand All@@ -39,7 +41,7 @@ class Foo:
assert_type(f, Foo)


def test_other_isdataclass_overloads(x: type, y: object) -> None:
def check_other_isdataclass_overloads(x: type, y: object) -> None:
# TODO: pyright correctly emits an error on this, but mypy does not -- why?
# dc.fields(x)

Expand All@@ -55,17 +57,23 @@ def test_other_isdataclass_overloads(x: type, y: object) -> None:
dc.replace(y) # type: ignore

if dc.is_dataclass(x):
assert_type(x, Type["DataclassInstance"])
assert_type(dc.fields(x), Tuple[dc.Field[Any], ...])
# These should cause type checkers to emit errors
# due to the fact it's a dataclass class, not an instance
dc.asdict(x) # type: ignore
dc.astuple(x) # type: ignore
dc.replace(x) # type: ignore

# Mypy correctly emits an error on these due to the fact
# that it's a dataclass class, not a dataclass instance.
# Pyright, however, handles ClassVar members in protocols differently.
# See https://github.com/microsoft/pyright/issues/4339
#
# dc.asdict(x)
# dc.astuple(x)
# dc.replace(x)
Comment on lines +63 to +70

@AlexWaygoodAlexWaygoodFeb 19, 2023

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We could possibly put these tests inside an if MYPY block, and add "defineConstant": { "MYPY": false } } to our pyrightconfig file for our test cases, to ensure that pyright doesn't check any code inside if MYPY blocks. I'm sort-of wary of doing that, however, as I'd really like to keep typechecker-specific test cases to a minimum in typeshed.


if dc.is_dataclass(y):
assert_type(y, Union["DataclassInstance", Type["DataclassInstance"]])
assert_type(dc.fields(y), Tuple[dc.Field[Any], ...])

# Mypy corrextly emits an error on these due to the fact we don't know
# Mypy correctly emits an error on these due to the fact we don't know
# whether it's a dataclass class or a dataclass instance.
# Pyright, however, handles ClassVar members in protocols differently.
# See https://github.com/microsoft/pyright/issues/4339
Expand All@@ -75,6 +83,7 @@ def test_other_isdataclass_overloads(x: type, y: object) -> None:
# dc.replace(y)

if dc.is_dataclass(y) and not isinstance(y, type):
assert_type(y, "DataclassInstance")
assert_type(dc.fields(y), Tuple[dc.Field[Any], ...])
assert_type(dc.asdict(y), Dict[str, Any])
assert_type(dc.astuple(y), Tuple[Any, ...])
Expand Down