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[ty] Synthesize __delitem__ for TypedDict to allow deleting non-required keys (#22122)

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## Summary

TypedDict now synthesizes a proper `__delitem__` method that...

- ...allows deletion of `NotRequired` keys and keys in `total=False`
TypedDicts.
- ...rejects deletion of required keys (synthesizes `__delitem__(k:
Never)`).
This commit is contained in:
Charlie Marsh
2025-12-23 22:39:54 -05:00
committed by GitHub
parent acdda78189
commit 969c8a547e
2 changed files with 85 additions and 7 deletions
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36
crates/ty_python_semantic/resources/mdtest/del.md
View File

@@ -239,21 +239,43 @@ del g[0]
### TypedDict deletion
Deleting a required key from a TypedDict is a type error because it would make the object no longer
a valid instance of that TypedDict type.
a valid instance of that TypedDict type. However, deleting `NotRequired` keys (or keys in
`total=False` TypedDicts) is allowed.
```py
from typing_extensions import TypedDict
from typing_extensions import TypedDict, NotRequired
class Movie(TypedDict):
name: str
year: int
m: Movie = {"name": "Blade Runner", "year": 1982}
class PartialMovie(TypedDict, total=False):
name: str
year: int
class MixedMovie(TypedDict):
name: str
year: NotRequired[int]
m: Movie = {"name": "Blade Runner", "year": 1982}
p: PartialMovie = {"name": "Test"}
mixed: MixedMovie = {"name": "Test"}
# Required keys cannot be deleted.
# error: [invalid-argument-type]
del m["name"]
```
TODO: Deletion of `NotRequired` keys (or keys in `total=False` TypedDicts) should be allowed, but ty
currently uses the typeshed stub `__delitem__(k: Never)` which rejects all deletions. See
mypy/pyright behavior for reference.
# In a partial TypedDict (`total=False`), all keys can be deleted.
del p["name"]
# `NotRequired` keys can always be deleted.
del mixed["year"]
# But required keys in mixed `TypedDict` still cannot be deleted.
# error: [invalid-argument-type]
del mixed["name"]
# And keys that don't exist cannot be deleted.
# error: [invalid-argument-type]
del mixed["non_existent"]
```

56
crates/ty_python_semantic/src/types/class.rs
View File

@@ -2818,6 +2818,62 @@ impl<'db> ClassLiteral<'db> {
CallableTypeKind::FunctionLike,
)))
}
(CodeGeneratorKind::TypedDict, "__delitem__") => {
let fields = self.fields(db, specialization, field_policy);
// Only non-required fields can be deleted. Required fields cannot be deleted
// because that would violate the TypedDict's structural type.
let mut deletable_fields = fields
.iter()
.filter(|(_, field)| !field.is_required())
.peekable();
if deletable_fields.peek().is_none() {
// If there are no deletable fields (all fields are required), synthesize a
// `__delitem__` that takes a `key` of type `Never` to signal that no keys
// can be deleted.
return Some(Type::Callable(CallableType::new(
db,
CallableSignature::single(Signature::new(
Parameters::new(
db,
[
Parameter::positional_only(Some(Name::new_static("self")))
.with_annotated_type(instance_ty),
Parameter::positional_only(Some(Name::new_static("key")))
.with_annotated_type(Type::Never),
],
),
Some(Type::none(db)),
)),
CallableTypeKind::FunctionLike,
)));
}
// Otherwise, add overloads for all deletable fields.
let overloads = deletable_fields.map(|(name, _field)| {
let key_type = Type::StringLiteral(StringLiteralType::new(db, name.as_str()));
Signature::new(
Parameters::new(
db,
[
Parameter::positional_only(Some(Name::new_static("self")))
.with_annotated_type(instance_ty),
Parameter::positional_only(Some(Name::new_static("key")))
.with_annotated_type(key_type),
],
),
Some(Type::none(db)),
)
});
Some(Type::Callable(CallableType::new(
db,
CallableSignature::from_overloads(overloads),
CallableTypeKind::FunctionLike,
)))
}
(CodeGeneratorKind::TypedDict, "get") => {
let overloads = self
.fields(db, specialization, field_policy)