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More precise return types forTypedDict.get#19897

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27e50e2
improved TypedDict.get inference
randolf-scholzAug 11, 2025
e708813
use original DictExpr test isntead of type-based
randolf-scholzSep 21, 2025
63224f2
removed second overload
randolf-scholzSep 22, 2025
808f593
added unit test for 19902
randolf-scholzSep 22, 2025
de8effe
Clarify overload comments in checkmember.py
randolf-scholzSep 23, 2025
4ebe192
check total/non-toal against union of keys
randolf-scholzSep 23, 2025
a9d2388
added incremental test
randolf-scholzSep 23, 2025
16c97ba
use appropriate namespace for TypedDict.get variable
randolf-scholzSep 23, 2025
628a0be
Merge branch 'master' into special_case_typeddict_get
randolf-scholzSep 23, 2025
443f6c7
Merge branch 'master' into special_case_typeddict_get
randolf-scholzSep 27, 2025
6bf9401
Merge branch 'master' into special_case_typeddict_get
randolf-scholzOct 4, 2025
cbbbd4d
Merge branch 'master' into special_case_typeddict_get
randolf-scholzOct 11, 2025
63f4975
revert reveal_type changes
randolf-scholzOct 12, 2025
f3e8556
Merge branch 'master' into special_case_typeddict_get
randolf-scholzOct 12, 2025
a0fbcee
Remove extra whitespace
ilevkivskyiOct 14, 2025
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revert reveal_type changes
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@randolf-scholz
randolf-scholz committedOct 12, 2025
commit63f49759f40316d2ef7ea1ad4c02199fa3bee92f
2 changes: 1 addition & 1 deletionmypy/checkexpr.py
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Expand Up@@ -1502,7 +1502,7 @@ def check_call_expr_with_callee_type(
def check_union_call_expr(self, e: CallExpr, object_type: UnionType, member: str) -> Type:
"""Type check calling a member expression where the base type is a union."""
res: list[Type] = []
for typ in object_type.relevant_items():
for typ inflatten_nested_unions(object_type.relevant_items()):
# Member access errors are already reported when visiting the member expression.
with self.msg.filter_errors():
item = analyze_member_access(
Expand Down
72 changes: 0 additions & 72 deletionsmypy/checkmember.py
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Expand Up@@ -17,7 +17,6 @@
from mypy.meet import is_overlapping_types
from mypy.messages import MessageBuilder
from mypy.nodes import (
ARG_OPT,
ARG_POS,
ARG_STAR,
ARG_STAR2,
Expand DownExpand Up@@ -69,7 +68,6 @@
TypedDictType,
TypeOfAny,
TypeType,
TypeVarId,
TypeVarLikeType,
TypeVarTupleType,
TypeVarType,
Expand DownExpand Up@@ -1406,76 +1404,6 @@ def analyze_typeddict_access(
fallback=mx.chk.named_type("builtins.function"),
name=name,
)
elif name == "get":
# synthesize TypedDict.get() overloads
str_type = mx.chk.named_type("builtins.str")
fn_type = mx.chk.named_type("builtins.function")
object_type = mx.chk.named_type("builtins.object")
type_info = typ.fallback.type
# type variable for default value
tvar = TypeVarType(
"T",
f"{type_info.fullname}.get.T",
id=TypeVarId(-1, namespace=f"{type_info.fullname}.get"),
values=[],
upper_bound=object_type,
default=AnyType(TypeOfAny.from_omitted_generics),
)
# generate the overloads
overloads: list[CallableType] = []
for key, value_type in typ.items.items():
key_type = LiteralType(key, fallback=str_type)

if key in typ.required_keys:
# If the key is required, we know it must be present in the TypedDict.
# def (K, object=...) -> V
overload = CallableType(
arg_types=[key_type, object_type],
arg_kinds=[ARG_POS, ARG_OPT],
arg_names=[None, None],
ret_type=value_type,
fallback=fn_type,
name=name,
)
overloads.append(overload)
else:
# The key is not required, but if it is present, we know its type.
# def (K) -> V | None (implicit default)
overload = CallableType(
arg_types=[key_type],
arg_kinds=[ARG_POS],
arg_names=[None],
ret_type=UnionType.make_union([value_type, NoneType()]),
fallback=fn_type,
name=name,
)
overloads.append(overload)

# def [T](K, T) -> V | T (explicit default)
overload = CallableType(
variables=[tvar],
arg_types=[key_type, tvar],
arg_kinds=[ARG_POS, ARG_POS],
arg_names=[None, None],
ret_type=UnionType.make_union([value_type, tvar]),
fallback=fn_type,
name=name,
)
overloads.append(overload)

# finally, add fallback overload when a key is used that is not in the TypedDict
# TODO: add support for extra items (PEP 728)
# def (str, object=...) -> object
fallback_overload = CallableType(
arg_types=[str_type, object_type],
arg_kinds=[ARG_POS, ARG_OPT],
arg_names=[None, None],
ret_type=object_type,
fallback=fn_type,
name=name,
)
overloads.append(fallback_overload)
return Overloaded(overloads)
return _analyze_member_access(name, typ.fallback, mx, override_info)


Expand Down
46 changes: 43 additions & 3 deletionsmypy/plugins/default.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -120,9 +120,9 @@ def get_function_signature_hook(
def get_method_signature_hook(
self, fullname: str
) -> Callable[[MethodSigContext], FunctionLike] | None:
# NOTE: signatures for `__setitem__`, `__delitem__` and `get` are
# defined in checkmember.py/analyze_typeddict_access
if fullname in TD_SETDEFAULT_NAMES:
if fullname == "typing.Mapping.get":
return typed_dict_get_signature_callback
elif fullname in TD_SETDEFAULT_NAMES:
return typed_dict_setdefault_signature_callback
elif fullname in TD_POP_NAMES:
return typed_dict_pop_signature_callback
Expand DownExpand Up@@ -212,6 +212,46 @@ def get_class_decorator_hook_2(
return None


def typed_dict_get_signature_callback(ctx: MethodSigContext) -> CallableType:
"""Try to infer a better signature type for TypedDict.get.

This is used to get better type context for the second argument that
depends on a TypedDict value type.
"""
signature = ctx.default_signature
if (
isinstance(ctx.type, TypedDictType)
and len(ctx.args) == 2
and len(ctx.args[0]) == 1
and isinstance(ctx.args[0][0], StrExpr)
and len(signature.arg_types) == 2
and len(signature.variables) == 1
and len(ctx.args[1]) == 1
):
key = ctx.args[0][0].value
value_type = get_proper_type(ctx.type.items.get(key))
ret_type = signature.ret_type
if value_type:
default_arg = ctx.args[1][0]
if (
isinstance(value_type, TypedDictType)
and isinstance(default_arg, DictExpr)
and len(default_arg.items) == 0
):
# Caller has empty dict {} as default for typed dict.
value_type = value_type.copy_modified(required_keys=set())
# Tweak the signature to include the value type as context. It's
# only needed for type inference since there's a union with a type
# variable that accepts everything.
tv = signature.variables[0]
assert isinstance(tv, TypeVarType)
return signature.copy_modified(
arg_types=[signature.arg_types[0], make_simplified_union([value_type, tv])],
ret_type=ret_type,
)
return signature


def typed_dict_get_callback(ctx: MethodContext) -> Type:
"""Infer a precise return type for TypedDict.get with literal first argument."""
if (
Expand Down
36 changes: 22 additions & 14 deletionstest-data/unit/check-typeddict.test
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Expand Up@@ -1007,12 +1007,12 @@ class D(TypedDict):
b: NotRequired[str]

def test(d: D) -> None:
reveal_type(d.get) # N: Revealed type is\
"Overload(\
def (Literal['a'], builtins.object =) -> builtins.int, \
def (Literal['b']) -> Union[builtins.str, None], \
def [T] (Literal['b'], T`-1) -> Union[builtins.str, T`-1], \
def (builtins.str, builtins.object =) -> builtins.object)"
reveal_type(d.get) # N: Revealed type is"Overload(def (k: builtins.str) -> builtins.object, def (builtins.str, builtins.object) -> builtins.object, def [V] (builtins.str, V`4) -> builtins.object)"






[builtins fixtures/dict.pyi]
[typing fixtures/typing-typeddict.pyi]
Expand DownExpand Up@@ -1155,21 +1155,29 @@ reveal_type(d.get('x', a)) # N: Revealed type is "Union[builtins.list[builtins.i
from typing import TypedDict
D = TypedDict('D', {'x': int, 'y': str})
d: D
d.get() # E: All overload variants of "get" require at least one argument \
d.get() # E: All overload variants of "get"of "Mapping"require at least one argument \
# N: Possible overload variants: \
# N: def get(Literal['x'], object = ..., /) ->int \
# N: def get(Literal['y'], object = ..., /) ->str \
# N: def get(str,object = ..., /) -> object
d.get('x', 1, 2) # E: No overload variant of "get" matches argument types "str", "int", "int" \
# N: def get(self, k: str) ->object \
# N: def get(self, str, object, /) ->object \
# N: def[V]get(self,str,V, /) -> object
d.get('x', 1, 2) # E: No overload variant of "get"of "Mapping"matches argument types "str", "int", "int" \
# N: Possible overload variants: \
# N: def get(Literal['x'], object = ..., /) ->int \
# N: def get(Literal['y'], object = ..., /) ->str \
# N: def get(str,object = ..., /) -> object
# N: def get(self, k: str) ->object \
# N: def get(self, str, object, /) ->object \
# N: def[V]get(self,str,Union[int, V], /) -> object
x = d.get('z')
reveal_type(x) # N: Revealed type is "builtins.object"
s = ''
y = d.get(s)
reveal_type(y) # N: Revealed type is "builtins.object"








[builtins fixtures/dict.pyi]
[typing fixtures/typing-typeddict.pyi]

Expand Down
4 changes: 3 additions & 1 deletiontest-data/unit/fixtures/typing-typeddict.pyi
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Expand Up@@ -56,7 +56,9 @@ class Mapping(Iterable[T], Generic[T, T_co], metaclass=ABCMeta):
@overload
def get(self, k: T) -> Optional[T_co]: pass
@overload
def get(self, k: T, default: Union[T_co, V]) -> Union[T_co, V]: pass
def get(self, k: T, default: T_co, /) -> Optional[T_co]: pass # type: ignore[misc]
@overload
def get(self, k: T, default: V, /) -> Union[T_co, V]: pass
def values(self) -> Iterable[T_co]: pass # Approximate return type
def __len__(self) -> int: ...
def __contains__(self, arg: object) -> int: pass
Expand Down
18 changes: 8 additions & 10 deletionstest-data/unit/pythoneval.test
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Expand Up@@ -1056,22 +1056,20 @@ def test_not_total(d: D_not_total) -> None:
_testTypedDictGet.py:8: note: Revealed type is "builtins.int"
_testTypedDictGet.py:9: note: Revealed type is "builtins.str"
_testTypedDictGet.py:10: note: Revealed type is "builtins.object"
_testTypedDictGet.py:11: error: All overload variants of "get" require at least one argument
_testTypedDictGet.py:11: error: All overload variants of "get"of "Mapping"require at least one argument
_testTypedDictGet.py:11: note: Possible overload variants:
_testTypedDictGet.py:11: note: def get(Literal['x'], object = ..., /) ->int
_testTypedDictGet.py:11: note: def get(Literal['y'], object = ..., /) ->str
_testTypedDictGet.py:11: note: def get(str, object = ..., /) -> object
_testTypedDictGet.py:11: note: def get(self, str, /) ->object
_testTypedDictGet.py:11: note: def get(self, str, /, default: object) ->object
_testTypedDictGet.py:11: note: def[_T]get(self, str, /, default: _T) -> object
_testTypedDictGet.py:13: note: Revealed type is "builtins.object"
_testTypedDictGet.py:16: note: Revealed type is "Union[builtins.int, None]"
_testTypedDictGet.py:17: note: Revealed type is "Union[builtins.str, None]"
_testTypedDictGet.py:18: note: Revealed type is "builtins.object"
_testTypedDictGet.py:19: error: All overload variants of "get" require at least one argument
_testTypedDictGet.py:19: error: All overload variants of "get"of "Mapping"require at least one argument
_testTypedDictGet.py:19: note: Possible overload variants:
_testTypedDictGet.py:19: note: def get(Literal['x'], /) -> Optional[int]
_testTypedDictGet.py:19: note: def [T] get(Literal['x'], T, /) -> Union[int, T]
_testTypedDictGet.py:19: note: def get(Literal['y'], /) -> Optional[str]
_testTypedDictGet.py:19: note: def [T] get(Literal['y'], T, /) -> Union[str, T]
_testTypedDictGet.py:19: note: def get(str, object = ..., /) -> object
_testTypedDictGet.py:19: note: def get(self, str, /) -> object
_testTypedDictGet.py:19: note: def get(self, str, /, default: object) -> object
_testTypedDictGet.py:19: note: def [_T] get(self, str, /, default: _T) -> object
_testTypedDictGet.py:21: note: Revealed type is "builtins.object"

[case testTypedDictMappingMethods]
Expand Down
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