ruff/crates/ty_python_semantic/resources/mdtest/annotations/any.md

Any

Annotation

typing.Any is a way to name the Any type.

from typing import Any

x: Any = 1
x = "foo"

def f():
    reveal_type(x)  # revealed: Any

Aliased to a different name

If you alias typing.Any to another name, we still recognize that as a spelling of the Any type.

from typing import Any as RenamedAny

x: RenamedAny = 1
x = "foo"

def f():
    reveal_type(x)  # revealed: Any

Shadowed class

If you define your own class named Any, using that in a type expression refers to your class, and isn't a spelling of the Any type.

class Any: ...

x: Any

def f():
    reveal_type(x)  # revealed: Any

# This verifies that we're not accidentally seeing typing.Any, since str is assignable
# to that but not to our locally defined class.
y: Any = "not an Any"  # error: [invalid-assignment]

Subclasses of Any

The spec allows you to define subclasses of Any.

SubclassOfAny has an unknown superclass, which might be int. The assignment to x should not be allowed, even when the unknown superclass is int. The assignment to y should be allowed, since Subclass might have int as a superclass, and is therefore assignable to int.

from typing import Any

class SubclassOfAny(Any): ...

reveal_type(SubclassOfAny.__mro__)  # revealed: tuple[Literal[SubclassOfAny], Any, Literal[object]]

x: SubclassOfAny = 1  # error: [invalid-assignment]
y: int = SubclassOfAny()

SubclassOfAny should not be assignable to a final class though, because SubclassOfAny could not possibly be a subclass of FinalClass:

from typing import final

@final
class FinalClass: ...

f: FinalClass = SubclassOfAny()  # error: [invalid-assignment]

@final
class OtherFinalClass: ...

f: FinalClass | OtherFinalClass = SubclassOfAny()  # error: [invalid-assignment]

A subclass of Any can also be assigned to arbitrary Callable and Protocol types:

from typing import Callable, Any, Protocol

def takes_callable1(f: Callable):
    f()

takes_callable1(SubclassOfAny())

def takes_callable2(f: Callable[[int], None]):
    f(1)

takes_callable2(SubclassOfAny())

class CallbackProtocol(Protocol):
    def __call__(self, x: int, /) -> None: ...

def takes_callback_proto(f: CallbackProtocol):
    f(1)

takes_callback_proto(SubclassOfAny())

class OtherProtocol(Protocol):
    x: int
    @property
    def foo(self) -> bytes: ...
    @foo.setter
    def foo(self, x: str) -> None: ...

def takes_other_protocol(f: OtherProtocol): ...

takes_other_protocol(SubclassOfAny())

A subclass of Any cannot be assigned to literal types, since those can not be subclassed:

from typing import Any, Literal

class MockAny(Any):
    pass

x: Literal[1] = MockAny()  # error: [invalid-assignment]

A use case where subclasses of Any come up is in mocking libraries, where the mock object should be assignable to (almost) any type:

from unittest.mock import MagicMock

x: int = MagicMock()

Invalid

Any cannot be parameterized:

from typing import Any

# error: [invalid-type-form] "Type `typing.Any` expected no type parameter"
def f(x: Any[int]):
    reveal_type(x)  # revealed: Unknown