# Any

## Annotation

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

```py
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.

```py
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.

```py
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`.

```py
from typing import Any
from ty_extensions import reveal_mro

class SubclassOfAny(Any): ...

reveal_mro(SubclassOfAny)  # revealed: (<class 'SubclassOfAny'>, Any, <class '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`:

```py
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:

```py
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 cannot be subclassed:

```py
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:

```py
from unittest.mock import MagicMock

x: int = MagicMock()
```

## Runtime properties

`typing.Any` is a class at runtime on Python 3.11+, and `typing_extensions.Any` is always a class.
On earlier versions of Python, `typing.Any` was an instance of `typing._SpecialForm`, but this is
not currently modeled by ty. We currently infer `Any` has having all attributes a class would have
on all versions of Python:

```py
from typing import Any
from ty_extensions import TypeOf, static_assert, is_assignable_to

reveal_type(Any.__base__)  # revealed: type | None
reveal_type(Any.__bases__)  # revealed: tuple[type, ...]
static_assert(is_assignable_to(TypeOf[Any], type))
```

## Invalid

`Any` cannot be parameterized:

```py
from typing import Any

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

`Any` cannot be called (this leads to a `TypeError` at runtime):

```py
Any()  # error: [call-non-callable] "Object of type `<special-form 'typing.Any'>` is not callable"
```

`Any` also cannot be used as a metaclass (under the hood, this leads to an implicit call to `Any`):

```py
class F(metaclass=Any): ...  # error: [invalid-metaclass] "Metaclass type `<special-form 'typing.Any'>` is not callable"
```

And `Any` cannot be used in `isinstance()` checks:

```py
# error: [invalid-argument-type] "`typing.Any` cannot be used with `isinstance()`: This call will raise `TypeError` at runtime"
isinstance("", Any)
```

The same applies when `Any` is nested inside a tuple, including non-literal tuples:

```py
isinstance("", (int, Any))  # error: [invalid-argument-type]
isinstance("", (int, (str, Any)))  # error: [invalid-argument-type]
classes = (int, Any)
isinstance("", classes)  # error: [invalid-argument-type]
```

But `issubclass()` checks are fine:

```py
issubclass(object, Any)  # no error!
issubclass(object, (int, Any))  # no error!
issubclass(object, (int, (str, Any)))  # no error!
```
