test-data/unit/check-final.test

-- Test cases for final qualifier
--

-- Definitions

[case testFinalDefiningModuleVar]
from typing import Final

x: Final = int()
y: Final[float] = int()
z: Final[int] = int()
bad: Final[str] = int()  # E: Incompatible types in assignment (expression has type "int", variable has type "str")

reveal_type(x)  # N: Revealed type is "builtins.int"
reveal_type(y)  # N: Revealed type is "builtins.float"
reveal_type(z)  # N: Revealed type is "builtins.int"
[out]

[case testFinalDefiningInstanceVar]
from typing import Final

class C:
    x: Final = int()
    y: Final[float] = int()
    z: Final[int] = int()
    bad: Final[str] = int()  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
class D(C): pass

reveal_type(D.x)  # N: Revealed type is "builtins.int"
reveal_type(D.y)  # N: Revealed type is "builtins.float"
reveal_type(D.z)  # N: Revealed type is "builtins.int"
reveal_type(D().x)  # N: Revealed type is "builtins.int"
reveal_type(D().y)  # N: Revealed type is "builtins.float"
reveal_type(D().z)  # N: Revealed type is "builtins.int"
[out]

[case testFinalDefiningInstanceVarImplicit]
from typing import Final, Tuple, Any

class C:
    def __init__(self, x: Tuple[int, Any]) -> None:
        self.x: Final = x
        self.y: Final[float] = 1
reveal_type(C((1, 2)).x)  # N: Revealed type is "tuple[builtins.int, Any]"
reveal_type(C((1, 2)).y)  # N: Revealed type is "builtins.float"
[builtins fixtures/tuple.pyi]
[out]

[case testFinalBadDefinitionTooManyArgs]
from typing import Final

x: Final[int, str]  # E: Final name must be initialized with a value \
                    # E: Final[...] takes at most one type argument
reveal_type(x)  # N: Revealed type is "builtins.int"

class C:
    def __init__(self) -> None:
        self.x: Final[float, float] = 1  # E: Final[...] takes at most one type argument
reveal_type(C().x)  # N: Revealed type is "builtins.float"
[out]

[case testFinalInvalidDefinitions]
from typing import Final, Any

x = y = 1  # type: Final[float]  # E: Invalid final declaration
z: Any
z[0]: Final[int]  # E: Invalid final declaration \
                  # E: Unexpected type declaration
[out]

[case testFinalDefiningInstanceVarStubs]
# Allow skipping r.h.s.
import mod
[file mod.pyi]
from typing import Final

x: Final  # E: Type in Final[...] can only be omitted if there is an initializer
y: Final[int]
class C:
    x: Final  # E: Type in Final[...] can only be omitted if there is an initializer
    y: Final[int]
    def __init__(self) -> None:
        self.z: Final  # E: Type in Final[...] can only be omitted if there is an initializer

reveal_type(x)  # N: Revealed type is "Any"
reveal_type(C.x)  # N: Revealed type is "Any"
v: C
reveal_type(v.z)  # N: Revealed type is "Any"
[out]

[case testFinalDefiningFunc]
from typing import final

@final  # E: @final cannot be used with non-method functions
def f(x: int) -> None: ...
[out]

[case testFinalDefiningFuncOverloaded]
from typing import final, overload

@overload
def f(x: int) -> int: ...
@overload
def f(x: str) -> str: ...
@final  # E: @final cannot be used with non-method functions
def f(x):
    pass
[out]

[case testFinalDefiningMeth]
from typing import final

class C:
    @final
    def f(self, x: int) -> None: ...
reveal_type(C().f)  # N: Revealed type is "def (x: builtins.int)"
[out]

[case testFinalDefiningMethOverloaded]
from typing import final, overload

class C:
    @overload
    def f(self, x: int) -> int: ...
    @overload
    def f(self, x: str) -> str: ...
    @final
    def f(self, x):
        pass

    @overload
    def bad(self, x: int) -> int: ...
    @final  # E: @final should be applied only to overload implementation
    @overload
    def bad(self, x: str) -> str: ...
    def bad(self, x):
        pass

reveal_type(C().f)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
[out]

[case testFinalDefiningMethOverloadedStubs]
from mod import C

reveal_type(C().f)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
[file mod.pyi]
from typing import final, overload

class C:
    @final
    @overload
    def f(self, x: int) -> int: ...
    @overload
    def f(self, x: str) -> str: ...

    @overload
    def bad(self, x: int) -> int: ...
    @final  # E: In a stub file @final must be applied only to the first overload
    @overload
    def bad(self, x: str) -> str: ...

[case testFinalDefiningProperty]
from typing import final

class C:
    @final
    @property
    def f(self) -> int: pass
    @property
    @final
    def g(self) -> int: pass
reveal_type(C().f)  # N: Revealed type is "builtins.int"
reveal_type(C().g)  # N: Revealed type is "builtins.int"
[builtins fixtures/property.pyi]
[out]

[case testFinalDefiningOuterOnly]
from typing import Final, Callable, Tuple, Any
x: Tuple[Final]  # E: Final can be only used as an outermost qualifier in a variable annotation
y: Callable[[], Tuple[Final[int]]]  # E: Final can be only used as an outermost qualifier in a variable annotation
[builtins fixtures/tuple.pyi]
[out]

[case testFinalDefiningNotInMethod]
from typing import Final

def f(x: Final[int]) -> int: ...  # E: Final can be only used as an outermost qualifier in a variable annotation
def g(x: int) -> Final[int]: ...  # E: Final can be only used as an outermost qualifier in a variable annotation
[out]

[case testFinalDefiningNotInMethodExtensions]
# flags: --python-version 3.14
from typing_extensions import Final

def f(x: Final[int]) -> int: ...  # E: Final can be only used as an outermost qualifier in a variable annotation
def g(x: int) -> Final[int]: ...  # E: Final can be only used as an outermost qualifier in a variable annotation
[builtins fixtures/tuple.pyi]
[out]

[case testFinalDefiningNoRhs]
from typing import Final
x: Final  # E: Type in Final[...] can only be omitted if there is an initializer
y: Final[int]  # E: Final name must be initialized with a value
class C:
    x: Final  # E: Type in Final[...] can only be omitted if there is an initializer
    y: Final[int]  # E: Final name must be initialized with a value
    def __init__(self) -> None:
        self.z: Final  # E: Type in Final[...] can only be omitted if there is an initializer
reveal_type(x)  # N: Revealed type is "Any"
reveal_type(y)  # N: Revealed type is "builtins.int"
reveal_type(C().x)  # N: Revealed type is "Any"
reveal_type(C().y)  # N: Revealed type is "builtins.int"
reveal_type(C().z)  # N: Revealed type is "Any"
[out]

[case testFinalDefiningNoRhsSubclass]
from typing import Final

class A:
    x: Final[int]  # E: Final name must be initialized with a value

class B(A):
    x = 1  # E: Cannot assign to final name "x"
    def __init__(self) -> None:
        self.x = 1  # E: Cannot assign to final attribute "x"
[out]

[case testFinalDefiningNoTypevarsExplicit]
from typing import Final, TypeVar, Generic, Tuple, Any

T = TypeVar('T')
d: Any

class C(Generic[T]):
    x: Final[Tuple[T, T]] = d  # E: Final name declared in class body cannot depend on type variables
[builtins fixtures/tuple.pyi]
[out]

[case testFinalDefiningTypevarsImplicit]
from typing import Final, TypeVar, Generic, Tuple, Any

T = TypeVar('T')

class C(Generic[T]):
    def __init__(self, x: Tuple[T, T]) -> None:
        self.x: Final = x
        self.y: Final = 1

reveal_type(C((1, 2)).x)  # N: Revealed type is "tuple[builtins.int, builtins.int]"
C.x  # E: Cannot access final instance attribute "x" on class object \
     # E: Access to generic instance variables via class is ambiguous
C.y  # E: Cannot access final instance attribute "y" on class object
[builtins fixtures/tuple.pyi]
[out]

[case testFinalDefiningNotInOtherMethod]
from typing import Final, Any, Tuple

class C:
    def meth(self, x: Tuple[int, Any]) -> None:
        self.x: Final = x  # E: Can only declare a final attribute in class body or __init__
        self.y: Final[float] = 1  # E: Can only declare a final attribute in class body or __init__
[builtins fixtures/tuple.pyi]
[out]

[case testFinalDefiningOnlyOnSelf]
from typing import Final, Any, Tuple

class U:
    x: Any
    y: Any
class C:
    def __init__(self, x: Tuple[int, Any]) -> None:
        slf = U()
        slf.x: Final = x  # E: Final can be only applied to a name or an attribute on self
        slf.y: Final[float] = 1  # E: Type cannot be declared in assignment to non-self attribute \
                                 # E: Final can be only applied to a name or an attribute on self
[builtins fixtures/tuple.pyi]
[out]

[case testFinalNotInProtocol]
from typing import Final, final, Protocol, overload

class P(Protocol):
    x: Final[float] = 1  # E: Protocol member cannot be final
    @final  # E: Protocol member cannot be final
    def meth(self, x) -> int:
        pass
    @overload
    def other(self, x: int) -> int: ...
    @overload
    def other(self, x: str) -> str: ...
    @final  # E: Protocol member cannot be final
    def other(self, x):
        pass
[out]

[case testFinalInProtocol]
from typing import Final, Protocol, final

class P(Protocol):
    var1 : Final[int] = 0 # E: Protocol member cannot be final

    @final # E: Protocol member cannot be final
    def meth1(self) -> None:
        var2: Final = 0

    def meth2(self) -> None:
        var3: Final = 0

    def meth3(self) -> None:
        class Inner:
            var3: Final = 0  # OK

            @final
            def inner(self) -> None: ...

    class Inner:
        var3: Final = 0  # OK

        @final
        def inner(self) -> None: ...

[out]

[case testFinalWithClassVarInProtocol]
from typing import Protocol, Final, final, ClassVar

class P(Protocol):
    var1 : Final[ClassVar[int]] = 0 # E: Variable should not be annotated with both ClassVar and Final
    var2: ClassVar[int] = 1

    @final # E: Protocol member cannot be final
    def meth1(self) -> None:
        ...

    def meth2(self) -> None:
        var3: Final[ClassVar[int]] = 0 # E: Variable should not be annotated with both ClassVar and Final # E: ClassVar can only be used for assignments in class body

[out]

[case testFinalNotInLoops]
from typing import Final

for i in [1, 2, 3]:
    x: Final = i  # E: Cannot use Final inside a loop

while True:
    y: Final = True  # E: Cannot use Final inside a loop
[builtins fixtures/list.pyi]
[out]

[case testFinalDelayedDefinition]
from typing import Final

class C:
    x: Final[int]  # OK, defined in __init__
    bad: Final[int]  # E: Final name must be initialized with a value

    def __init__(self, x: int) -> None:
        self.x = x  # OK, deferred definition
        self.x = 2  # E: Cannot assign to final attribute "x"

    def meth(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"

c: C
c.x = 3  # E: Cannot assign to final attribute "x"
class D(C):
    x = 4  # E: Cannot assign to final name "x"
d: D
d.x = 5  # E: Cannot assign to final attribute "x"
[out]

[case testFinalDelayedDefinitionOtherMethod]
from typing import Final

class C:
    x: Final[int]  # E: Final name must be initialized with a value

    def meth(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"
[out]

-- Reassignments

[case testFinalReassignModuleVar]
# flags: --allow-redefinition-old
from typing import Final

x: Final = 1
x
x = 2  # E: Cannot assign to final name "x"
def f() -> int:
    global x
    x = 3  # No error here is okay since we reported an error above
    return x

x2: Final = 1
x2
def f2() -> None:
    global x2
    x2 = 1  # E: Cannot assign to final name "x2"

y = 1
y
y: Final = 2  # E: Cannot redefine an existing name as final
y = 3  # E: Cannot assign to final name "y"

z: Final = 1
z: Final = 2  # E: Cannot redefine an existing name as final
z = 3  # E: Cannot assign to final name "z"

[case testFinalReassignModuleVar2]
# flags: --allow-redefinition-old
from typing import Final

x: Final = 1
x
def f() -> int:
    global x
    x = 3  # E: Cannot assign to final name "x"
    return x

y = 1
y
y = 2
y
y: Final = 3  # E: Cannot redefine an existing name as final

[case testFinalReassignModuleVar3]
# flags: --disallow-redefinition-old
from typing import Final

x: Final = 1
x
x = 2  # E: Cannot assign to final name "x"
def f() -> int:
    global x
    x = 3  # E: Cannot assign to final name "x"
    return x

x2: Final = 1
x2
def f2() -> None:
    global x2
    x2 = 1  # E: Cannot assign to final name "x2"

y = 1 # E: Cannot assign to final name "y"
y
y: Final = 2  # E: Cannot redefine an existing name as final
y = 3  # E: Cannot assign to final name "y"

z: Final = 1
z: Final = 2  # E: Cannot redefine an existing name as final
z = 3  # E: Cannot assign to final name "z"

[case testFinalReassignModuleReexport]
from typing import Final

from lib import X
from lib.mod import ID

X = 1  # E: Cannot assign to final name "X"
ID: Final = 1  # E: Cannot redefine an existing name as final
ID = 1  # E: Cannot assign to final name "ID"
[file lib/__init__.pyi]
from lib.const import X as X

[file lib/mod.pyi]
from lib.const import *

[file lib/const.pyi]
from typing import Final

ID: Final  # E: Type in Final[...] can only be omitted if there is an initializer
X: Final[int]

[case testFinalReassignFuncScope]
from typing import Final

def f() -> None:
    nl: Final = 0
    x: Final = 1
    x = 1  # E: Cannot assign to final name "x"

    y: Final = 1
    y: Final = 2  # E: Cannot redefine an existing name as final
    def nested() -> None:
        nonlocal nl
        nl = 1  # E: Cannot assign to final name "nl"
[out]

[case testFinalReassignModuleVarExternal]
import mod
mod.x = 2  # E: Cannot assign to final name "x"
[file mod.pyi]
from typing import Final
x: Final[int]
[out]

[case testFinalReassignInstanceVarClassBody]
from typing import Final

class C:
    x: Final = 1
    x = 2  # E: Cannot assign to final name "x"

    y = 1  # E: Cannot assign to final name "y"
    y: Final = 2  # E: Cannot redefine an existing name as final
[out]

[case testFinalReassignInstanceVarInit]
from typing import Final

class C:
    def __init__(self) -> None:
        self.x: Final = 1
        self.y = 1
        self.y: Final = 2  # E: Cannot redefine an existing name as final
    def meth(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"
[out]

[case testFinalReassignInstanceVarClassVsInit]

from typing import Final

class C:
    y: Final = 1
    def __init__(self) -> None:
        # Methods are processed after top-level in new analyzer.
        self.x: Final = 1  # E: Cannot redefine an existing name as final
        self.y = 2  # E: Cannot assign to final attribute "y"
    x = 2
[out]

[case testFinalReassignInstanceVarMethod]
from typing import Final

class C:
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
    def meth(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"
        self.y = 2  # E: Cannot assign to final attribute "y"
    def other(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"
        self.y = 2  # E: Cannot assign to final attribute "y"
    @classmethod
    def cm(cls) -> None:
        cls.x = 2  # E: Cannot assign to final attribute "x"
        cls.y  # E: Cannot access final instance attribute "y" on class object
[builtins fixtures/classmethod.pyi]
[out]

[case testFinalReassignInstanceVarExternalClass]
from typing import Final

class C:
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1

class D(C): pass

C.x = 2  # E: Cannot assign to final attribute "x"
D.x = 2  # E: Cannot assign to final attribute "x"
D.y = 2  # E: Cannot access final instance attribute "y" on class object \
         # E: Cannot assign to final attribute "y"
[out]

[case testFinalReassignInstanceVarExternalInstance]
from typing import Final

class C:
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1

class D(C): pass

C().x = 2  # E: Cannot assign to final attribute "x"
D().x = 2  # E: Cannot assign to final attribute "x"
D().y = 2  # E: Cannot assign to final attribute "y"
[out]

[case testFinalWorksWithComplexTargets]
from typing import Final, Any

y: Final[Any] = 1
x = a, (b, y), c = 2, (2, 2), 2  # E: Cannot assign to final name "y"
t, *y, s = u = [2, 2, 2]  # E: Cannot assign to final name "y"
[builtins fixtures/list.pyi]
[out]

[case testFinalInplaceAssign]
from typing import Final

class A:  # no such things in fixtures
    def __add__(self, other: A) -> A: ...
class B:
    def __add__(self, other: B) -> B: ...
    def __iadd__(self, other: B) -> B: ...

a: Final = A()
b: Final = B()
class C:
    a: Final = A()
    b: Final = B()
class D(C):
    pass

a += A()  # E: Cannot assign to final name "a"
b += B()  # E: Cannot assign to final name "b"
D().a += A()  # E: Cannot assign to final attribute "a"
D().b += B()  # E: Cannot assign to final attribute "b"
[out]

-- Overriding

[case testFinalOverridingVarClassBody]
from typing import Final

# We use properties in this tests and below because we want to check
# that any existing variable before final doesn't affect logic of
# subsequent overrides but writable attributes cannot be overridden by final.
class A:
    @property
    def x(self) -> int: ...
    @property
    def y(self) -> int: ...

class B(A):
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
class C(B):
    x: int = 2  # E: Cannot assign to final name "x"
    y: int = 2  # E: Cannot assign to final name "y"
    x = 3  # E: Cannot assign to final name "x"
    y = 3  # E: Cannot assign to final name "y"
class D(C):
    pass
D.x = 4  # E: Cannot assign to final attribute "x"
D.y = 4  # E: Cannot assign to final attribute "y"
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarClassBodyExplicit]
from typing import Final

class A:
    @property
    def x(self) -> int: ...
    @property
    def y(self) -> int: ...
class B(A):
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
class C(B):
    x: Final = 2  # E: Cannot override final attribute "x" (previously declared in base class "B")
    y: Final = 2  # E: Cannot override final attribute "y" (previously declared in base class "B")
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarInit]
from typing import Final

class A:
    @property
    def x(self) -> int: ...
    @property
    def y(self) -> int: ...
class B(A):
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
class C(B):
    def __init__(self) -> None:
        self.x = 2  # E: Cannot assign to final attribute "x"
        self.y = 2  # E: Cannot assign to final attribute "y"
    def meth(self) -> None:
        self.x = 3  # E: Cannot assign to final attribute "x"
        self.y = 3  # E: Cannot assign to final attribute "y"
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarInit2]
from typing import Final

class A:
    @property
    def x(self) -> int: ...
    @property
    def y(self) -> int: ...
class B(A):
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
class C(B):
    def __init__(self) -> None:
        self.x: Final = 2  # E: Cannot override final attribute "x" (previously declared in base class "B")
        self.y: Final = 2  # E: Cannot override final attribute "y" (previously declared in base class "B")
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarOtherMethod]
from typing import Final

class A:
    @property
    def x(self) -> int: ...
    @property
    def y(self) -> int: ...
class B(A):
    x: Final = 1
    def __init__(self) -> None:
        self.y: Final = 1
class C(B):
    def meth(self) -> None:
        self.x: int = 2    # E: Cannot assign to final attribute "x"
        self.y: int = 2    # E: Cannot assign to final attribute "y"

        self.x = 3  # E: Cannot assign to final attribute "x"
        self.y = 3  # E: Cannot assign to final attribute "y"
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarMultipleInheritanceClass]
from typing import Final, Any

class A:
    x: Final[Any] = 1
class B:
    @property
    def x(self) -> int: ...
class C(A, B): ...
class D(B, A): ...  # E: Cannot override final attribute "x" (previously declared in base class "A")
C.x = 3  # E: Cannot assign to final attribute "x"
C().x = 4  # E: Cannot assign to final attribute "x"
D().x = 4  # E: Cannot assign to final attribute "x" \
           # E: Property "x" defined in "B" is read-only
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarMultipleInheritanceInit]
from typing import Final, Any

class A:
    def __init__(self) -> None:
        self.x: Final[Any] = 1
class B:
    @property
    def x(self) -> int: ...
class C(A, B): ...
class D(B, A): ...  # E: Cannot override final attribute "x" (previously declared in base class "A")
C.x = 3  # E: Cannot access final instance attribute "x" on class object \
         # E: Cannot assign to final attribute "x"
C().x = 4  # E: Cannot assign to final attribute "x"
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarMultipleInheritanceMixed]
from typing import Final

class A:
    x: Final = 1
class B:
    def __init__(self) -> None:
        self.x = 2
class C(A, B): ...  # E: Cannot override writable attribute "x" with a final one
class D(B, A): ...  # E: Cannot override final attribute "x" (previously declared in base class "A")
C.x = 3  # E: Cannot assign to final attribute "x"
D.x = 3  # E: Cannot assign to final attribute "x"
C().x = 4  # E: Cannot assign to final attribute "x"
D().x = 4  # E: Cannot assign to final attribute "x"
[out]

[case testFinalOverridingVarWithMethod]
from typing import Final, Any

class A:
    x: Final[Any] = 1
    def __init__(self) -> None:
        self.y: Final[Any] = 1

class B(A):
    def x(self) -> None: pass  # E: Cannot override final attribute "x" (previously declared in base class "A")
    def y(self) -> None: pass  # E: Cannot override final attribute "y" (previously declared in base class "A")

class C(A):
    @property  # E: Cannot override final attribute "x" (previously declared in base class "A")
    def x(self) -> None: pass
    @property  # E: Cannot override final attribute "y" (previously declared in base class "A")
    def y(self) -> None: pass
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingVarWithMethodClass]
from typing import Final, Any

class A:
    x: Final[Any] = 1
    def __init__(self) -> None:
        self.y: Final[Any] = 1

class B(A):
    @classmethod  # E: Cannot override final attribute "x" (previously declared in base class "A")
    def x(self) -> None: pass
    @classmethod  # E: Cannot override final attribute "y" (previously declared in base class "A")
    def y(self) -> None: pass

[builtins fixtures/classmethod.pyi]
[out]

[case testFinalOverridingMethodRegular]
from typing import final

class B:
    @final
    def meth(self) -> None: ...
class C(B):
    def meth(self) -> None: ...  # E: Cannot override final attribute "meth" (previously declared in base class "B")
[out]

[case testFinalOverridingMethodInitNew]
from typing import final

class B:
    @final
    def __init__(self) -> None: ...
    @final
    def __new__(cls) -> B: ...
class C(B):
    def __init__(self) -> None: ...  # E: Cannot override final attribute "__init__" (previously declared in base class "B")
    def __new__(cls) -> C: ...  # E: Cannot override final attribute "__new__" (previously declared in base class "B")
[out]

[case testFinalOverridingMethodWithVar]
from typing import final, Final, Any

a: Any

class A:
    @final
    def f(self) -> None: pass
    @final
    @property
    def p(self) -> int: pass

class B(A):
    f = a  # E: Cannot override final attribute "f" (previously declared in base class "A")
    p = a  # E: Cannot override final attribute "p" (previously declared in base class "A")
class C(A):
    f: Any  # E: Cannot override final attribute "f" (previously declared in base class "A")
    p: Any  # E: Cannot override final attribute "p" (previously declared in base class "A")
class D(A):
    f: Final = a  # E: Cannot override final attribute "f" (previously declared in base class "A")
    p: Final = a  # E: Cannot override final attribute "p" (previously declared in base class "A")
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingMethodWithVarImplicit]
from typing import final, Any, Final

a: Any

class A:
    @final
    def f(self) -> None: pass
    @final
    @classmethod
    def c(cls) -> int: pass

class B(A):
    def __init__(self) -> None:
        self.f: Any  # E: Cannot assign to final attribute "f" \
                     # E: Cannot override final attribute "f" (previously declared in base class "A")
        self.c: Any  # E: Cannot assign to final attribute "c" \
                     # E: Cannot override final attribute "c" (previously declared in base class "A")

B().f = a  # E: Cannot assign to final attribute "f"
B().c = a  # E: Cannot assign to final attribute "c"

class C(A):
    def __init__(self) -> None:
        self.f: Final = a  # E: Cannot override final attribute "f" (previously declared in base class "A")
        self.c: Final = a  # E: Cannot override final attribute "c" (previously declared in base class "A")
[builtins fixtures/classmethod.pyi]
[out]

[case testFinalCanOverrideMethodWithFinal]
from typing import final

class B:
    def meth(self) -> None: ...
class C(B):
    @final  # OK
    def meth(self) -> None: ...
[out]

[case testFinalOverridingMethodMultipleInheritance]
from typing import final

class A:
    def m(self) -> int: pass
class B:
    @final
    def m(self) -> int: pass

class C(A, B): pass  # E: Cannot override final attribute "m" (previously declared in base class "B")
class D(B, A): pass
[out]

[case testFinalOverridingMethodMultipleInheritanceVar]
from typing import final, Any

class A:
    m: Any
class B:
    @final
    def m(self) -> int: pass

class C(A, B): pass  # E: Cannot override final attribute "m" (previously declared in base class "B")
class D(B, A): pass  # E: Cannot override writable attribute "m" with a final one
[out]

[case testFinalOverridingClassMethod]
from typing import final

class B:
    @classmethod
    @final
    def f(cls) -> int: pass

class C(B):
    @classmethod  # E: Cannot override final attribute "f" (previously declared in base class "B")
    def f(cls) -> int: pass
[builtins fixtures/classmethod.pyi]
[out]

[case testFinalOverridingStaticMethod]
from typing import final

class B:
    @staticmethod
    @final
    def f() -> int: pass
    @final
    @staticmethod
    def g() -> int: pass

class C(B):
    @staticmethod  # E: Cannot override final attribute "f" (previously declared in base class "B")
    def f() -> int: pass
    @staticmethod  # E: Cannot override final attribute "g" (previously declared in base class "B")
    def g() -> int: pass
[builtins fixtures/staticmethod.pyi]
[out]

[case testFinalOverridingProperty]
from typing import final

class B:
    @final
    @property
    def f(self) -> int: pass
    @property
    @final
    def g(self) -> int: pass

class C(B):
    @property  # E: Cannot override final attribute "f" (previously declared in base class "B")
    def f(self) -> int: pass
    @property  # E: Cannot override final attribute "g" (previously declared in base class "B")
    def g(self) -> int: pass
[builtins fixtures/property.pyi]
[out]

[case testFinalOverridingMethodOverloads]
from typing import final, overload

class B:
    @overload
    def f(self, x: int) -> int: ...
    @overload
    def f(self, x: str) -> str: ...
    @final
    def f(self, x):
        pass

class C(B):
    @overload  # E: Cannot override final attribute "f" (previously declared in base class "B")
    def f(self, x: int) -> int: ...
    @overload
    def f(self, x: str) -> str: ...
    def f(self, x):
        pass
[out]

[case testFinalClassNoInheritance]
from typing import final

@final
class B: ...
class C(B):  # E: Cannot inherit from final class "B"
    pass
class D(C):  # E: Cannot inherit from final class "B"
    pass
[out]

[case testFinalClassNoInheritanceMulti]
from typing import final

class A: ...
@final
class B: ...
class C(B, A):  # E: Cannot inherit from final class "B"
    pass
class D(A, B):  # E: Cannot inherit from final class "B"
    pass
[out]

[case testFinalCantOverrideWriteable]
from typing import Any, Final, final

class B:
    x: Any
    @property
    def y(self) -> Any: ...
    @y.setter
    def y(self, x: Any) -> None: ...

class C(B):
    x: Final = 1  # E: Cannot override writable attribute "x" with a final one
    y: Final = 1  # E: Cannot override writable attribute "y" with a final one

class D(B):
    @final  # E: Cannot override writable attribute "x" with a final one
    def x(self) -> int: ...
    @final  # E: Cannot override writable attribute "y" with a final one
    def y(self) -> int: ...
[builtins fixtures/property.pyi]
[out]

[case testFinalCanUseTypingExtensions]
from typing_extensions import final, Final

x: Final = 1
x = 2  # E: Cannot assign to final name "x"

class S:
    x: Final = 1
S.x = 2  # E: Cannot assign to final attribute "x"

class B:
    @final
    def meth(self) -> None: ...
class C(B):
    def meth(self) -> None: ...  # E: Cannot override final attribute "meth" (previously declared in base class "B")

@final
class F: ...
class E(F): ...  # E: Cannot inherit from final class "F"
[builtins fixtures/tuple.pyi]
[out]

[case testFinalCanUseTypingExtensionsAliased]
from typing_extensions import final as f, Final as F

x: F = 1
x = 2  # E: Cannot assign to final name "x"

class S:
    x: F = 1
S.x = 2  # E: Cannot assign to final attribute "x"

class B:
    @f
    def meth(self) -> None: ...
class C(B):
    def meth(self) -> None: ...  # E: Cannot override final attribute "meth" (previously declared in base class "B")

@f
class D(C): ...
class E(D): ...  # E: Cannot inherit from final class "D"
[builtins fixtures/tuple.pyi]
[out]

[case testFinalMultiassignAllowed]
from typing import Final

class A:
    x: Final[int]
    y: Final[int]
    def __init__(self) -> None:
        self.x, self.y = 1, 2

class B:
    x: Final[int]
    y: Final[int]
    def __init__(self) -> None:
        self.x = self.y = 1
[out]

[case testFinalInDeferredMethod]
from typing import Final

class A:
    def __init__(self) -> None:
        self.x = 10  # type: Final
        undefined  # type: ignore
[builtins fixtures/tuple.pyi]

[case testFinalUsedWithClassVar]
# flags: --python-version 3.12
from typing import Final, ClassVar

class A:
    a: Final[ClassVar[int]]  # E: Variable should not be annotated with both ClassVar and Final
    b: ClassVar[Final[int]]  # E: Final can be only used as an outermost qualifier in a variable annotation
    c: ClassVar[Final] = 1  # E: Final can be only used as an outermost qualifier in a variable annotation
[out]

[case testFinalUsedWithClassVarAfterPy313]
# flags: --python-version 3.13
from typing import Final, ClassVar

class A:
    a: Final[ClassVar[int]] = 1
    b: ClassVar[Final[int]] = 1
    c: ClassVar[Final] = 1

[case testFinalClassWithAbstractMethod]
from typing import final
from abc import ABC, abstractmethod

@final
class A(ABC): # E: Final class __main__.A has abstract attributes "B"
    @abstractmethod
    def B(self) -> None: ...

[case testFinalDefiningFuncWithAbstractMethod]
from typing import final
from abc import ABC, abstractmethod

class A(ABC):
    @final # E: Method B is both abstract and final
    @abstractmethod
    def B(self) -> None: ...

[case testFinalClassVariableRedefinitionDoesNotCrash]
# This used to crash -- see #12950
from typing import Final

class MyClass:
    a: None
    a: Final[int] = 1  # E: Cannot redefine an existing name as final  # E: Name "a" already defined on line 5

[case testFinalOverrideAllowedForPrivate]
from typing import Final, final

class Parent:
    __foo: Final[int] = 0
    @final
    def __bar(self) -> None: ...

class Child(Parent):
    __foo: Final[int] = 1
    @final
    def __bar(self) -> None: ...

[case testFinalWithoutBool]
from typing import Literal, final

class A:
    pass

@final
class B:
    pass

@final
class C:
    def __len__(self) -> Literal[1]: return 1

reveal_type(A() and 42)  # N: Revealed type is "__main__.A | Literal[42]?"
reveal_type(B() and 42)  # N: Revealed type is "Literal[42]?"
reveal_type(C() and 42)  # N: Revealed type is "Literal[42]?"

[builtins fixtures/bool.pyi]

[case testFinalWithoutBoolButWithLen]
from typing import Literal, final

# Per Python data model, __len__ is called if __bool__ does not exist.
# In a @final class, __bool__ would not exist.

@final
class A:
    def __len__(self) -> int: ...

@final
class B:
    def __len__(self) -> Literal[1]: return 1

@final
class C:
    def __len__(self) -> Literal[0]: return 0

reveal_type(A() and 42)  # N: Revealed type is "__main__.A | Literal[42]?"
reveal_type(B() and 42)  # N: Revealed type is "Literal[42]?"
reveal_type(C() and 42)  # N: Revealed type is "__main__.C"

[builtins fixtures/bool.pyi]

[case testCanAccessFinalClassInit]
from typing import final

@final
class FinalClass:
    pass

def check_final_class() -> None:
    new_instance = FinalClass()
    new_instance.__init__()

class FinalInit:
    @final
    def __init__(self) -> None:
        pass

def check_final_init() -> None:
    new_instance = FinalInit()
    new_instance.__init__()
[builtins fixtures/tuple.pyi]

[case testNarrowingOfFinalInFunctionsNotSpecial]
from typing import Final, Union

def _init() -> Union[int, None]:
    return 0

FOO: Final = _init()

class Example:
    if FOO is not None:
        reveal_type(FOO)  # N: Revealed type is "builtins.int"

        def fn(self) -> int:
            return FOO  # E: Incompatible return value type (got "int | None", expected "int")

if FOO is not None:
    reveal_type(FOO)  # N: Revealed type is "builtins.int"

    def func() -> int:
        return FOO  # E: Incompatible return value type (got "int | None", expected "int")

[case testDisjointBase]
from typing_extensions import disjoint_base

@disjoint_base
class Disjoint1: pass

@disjoint_base
class Disjoint2: pass

@disjoint_base
class DisjointChild(Disjoint1): pass

class C1: pass
class C2(Disjoint1, C1): pass
class C3(DisjointChild, Disjoint1): pass

class C4(Disjoint1, Disjoint2):  # E: Class "C4" has incompatible disjoint bases
    pass

class C5(Disjoint2, Disjoint1):  # E: Class "C5" has incompatible disjoint bases
    pass

class C6(Disjoint2, DisjointChild):  # E: Class "C6" has incompatible disjoint bases
    pass

class C7(DisjointChild, Disjoint2):  # E: Class "C7" has incompatible disjoint bases
    pass

class C8(DisjointChild, Disjoint1, Disjoint2):  # E: Class "C8" has incompatible disjoint bases
    pass

class C9(C2, Disjoint2):  # E: Class "C9" has incompatible disjoint bases
    pass

class C10(C3, Disjoint2):  # E: Class "C10" has incompatible disjoint bases
    pass

[builtins fixtures/tuple.pyi]
[case testDisjointBaseSlots]
class S1:
    __slots__ = ("a",)

class S2:
    __slots__ = ("b",)

class S3:
    __slots__ = ()

class S4(S1):
    __slots__ = ("c",)

class S5(S1, S2):  # E: Class "S5" has incompatible disjoint bases
    pass

class S6(S1, S3): pass  # OK
class S7(S3, S1): pass  # OK

class S8(S4, S1): pass  # OK

class S9(S2, S4):  # E: Class "S9" has incompatible disjoint bases
    pass

[builtins fixtures/tuple.pyi]