Attributes

Tests for attribute access on various kinds of types.

Class and instance variables

Pure instance variables

Variable only declared/bound in `init`

Variables only declared and/or bound in __init__ are pure instance variables. They cannot be accessed on the class itself.

class C:
    def __init__(self, param: int | None, flag: bool = False) -> None:
        value = 1 if flag else "a"
        self.inferred_from_value = value
        self.inferred_from_other_attribute = self.inferred_from_value
        self.inferred_from_param = param
        self.declared_only: bytes
        self.declared_and_bound: bool = True
        if flag:
            self.possibly_undeclared_unbound: str = "possibly set in __init__"

c_instance = C(1)

reveal_type(c_instance.inferred_from_value)  # revealed: Unknown | Literal[1, "a"]

# TODO: Same here. This should be `Unknown | Literal[1, "a"]`
reveal_type(c_instance.inferred_from_other_attribute)  # revealed: Unknown

# TODO: should be `int | None`
reveal_type(c_instance.inferred_from_param)  # revealed: Unknown | int | None

reveal_type(c_instance.declared_only)  # revealed: bytes

reveal_type(c_instance.declared_and_bound)  # revealed: bool

# We probably don't want to emit a diagnostic for this being possibly undeclared/unbound.
# mypy and pyright do not show an error here.
reveal_type(c_instance.possibly_undeclared_unbound)  # revealed: str

# This assignment is fine, as we infer `Unknown | Literal[1, "a"]` for `inferred_from_value`.
c_instance.inferred_from_value = "value set on instance"

# This assignment is also fine:
c_instance.inferred_from_param = None

# TODO: this should be an error (incompatible types in assignment)
c_instance.inferred_from_param = "incompatible"

# TODO: we already show an error here but the message might be improved?
# mypy shows no error here, but pyright raises "reportAttributeAccessIssue"
# error: [unresolved-attribute] "Type `Literal[C]` has no attribute `inferred_from_value`"
reveal_type(C.inferred_from_value)  # revealed: Unknown

# TODO: this should be an error (pure instance variables cannot be accessed on the class)
# mypy shows no error here, but pyright raises "reportAttributeAccessIssue"
C.inferred_from_value = "overwritten on class"

# This assignment is fine:
c_instance.declared_and_bound = False

# TODO: After this assignment to the attribute within this scope, we may eventually want to narrow
# the `bool` type (see above) for this instance variable to `Literal[False]` here. This is unsound
# in general (we don't know what else happened to `c_instance` between the assignment and the use
# here), but mypy and pyright support this. In conclusion, this could be `bool` but should probably
# be `Literal[False]`.
reveal_type(c_instance.declared_and_bound)  # revealed: bool

Variable declared in class body and possibly bound in `init`

The same rule applies even if the variable is declared (not bound!) in the class body: it is still a pure instance variable.

class C:
    declared_and_bound: str | None

    def __init__(self) -> None:
        self.declared_and_bound = "value set in __init__"

c_instance = C()

reveal_type(c_instance.declared_and_bound)  # revealed: str | None

# TODO: we currently plan to emit a diagnostic here. Note that both mypy
# and pyright show no error in this case! So we may reconsider this in
# the future, if it turns out to produce too many false positives.
reveal_type(C.declared_and_bound)  # revealed: str | None

# TODO: same as above. We plan to emit a diagnostic here, even if both mypy
# and pyright allow this.
C.declared_and_bound = "overwritten on class"

# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `declared_and_bound` of type `str | None`"
c_instance.declared_and_bound = 1

Variable declared in class body and not bound anywhere

If a variable is declared in the class body but not bound anywhere, we still consider it a pure instance variable and allow access to it via instances.

class C:
    only_declared: str

c_instance = C()

reveal_type(c_instance.only_declared)  # revealed: str

# TODO: mypy and pyright do not show an error here, but we plan to emit a diagnostic.
# The type could be changed to 'Unknown' if we decide to emit an error?
reveal_type(C.only_declared)  # revealed: str

# TODO: mypy and pyright do not show an error here, but we plan to emit one.
C.only_declared = "overwritten on class"

Mixed declarations/bindings in class body and `init`

class C:
    only_declared_in_body: str | None
    declared_in_body_and_init: str | None

    declared_in_body_defined_in_init: str | None

    bound_in_body_declared_in_init = "a"

    bound_in_body_and_init = None

    def __init__(self, flag) -> None:
        self.only_declared_in_init: str | None
        self.declared_in_body_and_init: str | None = None

        self.declared_in_body_defined_in_init = "a"

        self.bound_in_body_declared_in_init: str | None

        if flag:
            self.bound_in_body_and_init = "a"

c_instance = C(True)

reveal_type(c_instance.only_declared_in_body)  # revealed: str | None
reveal_type(c_instance.only_declared_in_init)  # revealed: str | None
reveal_type(c_instance.declared_in_body_and_init)  # revealed: str | None

reveal_type(c_instance.declared_in_body_defined_in_init)  # revealed: str | None

reveal_type(c_instance.bound_in_body_declared_in_init)  # revealed: str | None

reveal_type(c_instance.bound_in_body_and_init)  # revealed: Unknown | None | Literal["a"]

Variable defined in non-`init` method

We also recognize pure instance variables if they are defined in a method that is not __init__.

class C:
    def __init__(self, param: int | None, flag: bool = False) -> None:
        self.initialize(param, flag)

    def initialize(self, param: int | None, flag: bool) -> None:
        value = 1 if flag else "a"
        self.inferred_from_value = value
        self.inferred_from_other_attribute = self.inferred_from_value
        self.inferred_from_param = param
        self.declared_only: bytes
        self.declared_and_bound: bool = True

c_instance = C(1)

reveal_type(c_instance.inferred_from_value)  # revealed: Unknown | Literal[1, "a"]

# TODO: Should be `Unknown | Literal[1, "a"]`
reveal_type(c_instance.inferred_from_other_attribute)  # revealed: Unknown

# TODO: Should be `int | None`
reveal_type(c_instance.inferred_from_param)  # revealed: Unknown | int | None

reveal_type(c_instance.declared_only)  # revealed: bytes

reveal_type(c_instance.declared_and_bound)  # revealed: bool

# TODO: We already show an error here, but the message might be improved?
# error: [unresolved-attribute]
reveal_type(C.inferred_from_value)  # revealed: Unknown

# TODO: this should be an error
C.inferred_from_value = "overwritten on class"

Variable defined in multiple methods

If we see multiple un-annotated assignments to a single attribute (self.x below), we build the union of all inferred types (and Unknown). If we see multiple conflicting declarations of the same attribute, that should be an error.

def get_int() -> int:
    return 0

def get_str() -> str:
    return "a"

class C:
    z: int

    def __init__(self) -> None:
        self.x = get_int()
        self.y: int = 1

    def other_method(self):
        self.x = get_str()

        # TODO: this redeclaration should be an error
        self.y: str = "a"

        # TODO: this redeclaration should be an error
        self.z: str = "a"

c_instance = C()

reveal_type(c_instance.x)  # revealed: Unknown | int | str
reveal_type(c_instance.y)  # revealed: int
reveal_type(c_instance.z)  # revealed: int

Attributes defined in tuple unpackings

def returns_tuple() -> tuple[int, str]:
    return (1, "a")

class C:
    a1, b1 = (1, "a")
    c1, d1 = returns_tuple()

    def __init__(self) -> None:
        self.a2, self.b2 = (1, "a")
        self.c2, self.d2 = returns_tuple()

c_instance = C()

reveal_type(c_instance.a1)  # revealed: Unknown | Literal[1]
reveal_type(c_instance.b1)  # revealed: Unknown | Literal["a"]
reveal_type(c_instance.c1)  # revealed: Unknown | int
reveal_type(c_instance.d1)  # revealed: Unknown | str

# TODO: This should be supported (no error; type should be: `Unknown | Literal[1]`)
# error: [unresolved-attribute]
reveal_type(c_instance.a2)  # revealed: Unknown

# TODO: This should be supported (no error; type should be: `Unknown | Literal["a"]`)
# error: [unresolved-attribute]
reveal_type(c_instance.b2)  # revealed: Unknown

# TODO: Similar for these two (should be `Unknown | int` and `Unknown | str`, respectively)
# error: [unresolved-attribute]
reveal_type(c_instance.c2)  # revealed: Unknown
# error: [unresolved-attribute]
reveal_type(c_instance.d2)  # revealed: Unknown

Attributes defined in for-loop (unpacking)

class IntIterator:
    def __next__(self) -> int:
        return 1

class IntIterable:
    def __iter__(self) -> IntIterator:
        return IntIterator()

class TupleIterator:
    def __next__(self) -> tuple[int, str]:
        return (1, "a")

class TupleIterable:
    def __iter__(self) -> TupleIterator:
        return TupleIterator()

class C:
    def __init__(self):
        for self.x in IntIterable():
            pass

        for _, self.y in TupleIterable():
            pass

# TODO: Pyright fully supports these, mypy detects the presence of the attributes,
# but infers type `Any` for both of them. We should infer `int` and `str` here:

# error: [unresolved-attribute]
reveal_type(C().x)  # revealed: Unknown

# error: [unresolved-attribute]
reveal_type(C().y)  # revealed: Unknown

Conditionally declared / bound attributes

We currently do not raise a diagnostic or change behavior if an attribute is only conditionally defined. This is consistent with what mypy and pyright do.

def flag() -> bool:
    return True

class C:
    def f(self) -> None:
        if flag():
            self.a1: str | None = "a"
            self.b1 = 1
    if flag():
        def f(self) -> None:
            self.a2: str | None = "a"
            self.b2 = 1

c_instance = C()

reveal_type(c_instance.a1)  # revealed: str | None
reveal_type(c_instance.a2)  # revealed: str | None
reveal_type(c_instance.b1)  # revealed: Unknown | Literal[1]
reveal_type(c_instance.b2)  # revealed: Unknown | Literal[1]

Methods that does not use `self` as a first parameter

class C:
    # This might trigger a stylistic lint like `invalid-first-argument-name-for-method`, but
    # it should be supported in general:
    def __init__(this) -> None:
        this.declared_and_bound: str | None = "a"

reveal_type(C().declared_and_bound)  # revealed: str | None

Aliased `self` parameter

class C:
    def __init__(self) -> None:
        this = self
        this.declared_and_bound: str | None = "a"

# This would ideally be `str | None`, but mypy/pyright don't support this either,
# so `Unknown` + a diagnostic is also fine.
# error: [unresolved-attribute]
reveal_type(C().declared_and_bound)  # revealed: Unknown

Static methods do not influence implicitly defined attributes

class Other:
    x: int

class C:
    @staticmethod
    def f(other: Other) -> None:
        other.x = 1

# error: [unresolved-attribute]
reveal_type(C.x)  # revealed: Unknown

# TODO: this should raise `unresolved-attribute` as well, and the type should be `Unknown`
reveal_type(C().x)  # revealed: Unknown | Literal[1]

# This also works if `staticmethod` is aliased:

my_staticmethod = staticmethod

class D:
    @my_staticmethod
    def f(other: Other) -> None:
        other.x = 1

# error: [unresolved-attribute]
reveal_type(D.x)  # revealed: Unknown

# TODO: this should raise `unresolved-attribute` as well, and the type should be `Unknown`
reveal_type(D().x)  # revealed: Unknown | Literal[1]

If staticmethod is something else, that should not influence the behavior:

other.py:

def staticmethod(f):
    return f

class C:
    @staticmethod
    def f(self) -> None:
        self.x = 1

reveal_type(C().x)  # revealed: Unknown | Literal[1]

And if staticmethod is fully qualified, that should also be recognized:

fully_qualified.py:

import builtins

class Other:
    x: int

class C:
    @builtins.staticmethod
    def f(other: Other) -> None:
        other.x = 1

# error: [unresolved-attribute]
reveal_type(C.x)  # revealed: Unknown

# TODO: this should raise `unresolved-attribute` as well, and the type should be `Unknown`
reveal_type(C().x)  # revealed: Unknown | Literal[1]

Attributes defined in statically-known-to-be-false branches

class C:
    def __init__(self) -> None:
        # We use a "significantly complex" condition here (instead of just `False`)
        # for a proper comparison with mypy and pyright, which distinguish between
        # conditions that can be resolved from a simple pattern matching and those
        # that need proper type inference.
        if (2 + 3) < 4:
            self.x: str = "a"

# TODO: Ideally, this would result in a `unresolved-attribute` error. But mypy and pyright
# do not support this either (for conditions that can only be resolved to `False` in type
# inference), so it does not seem to be particularly important.
reveal_type(C().x)  # revealed: str

Pure class variables (`ClassVar`)

Annotated with `ClassVar` type qualifier

Class variables annotated with the typing.ClassVar type qualifier are pure class variables. They cannot be overwritten on instances, but they can be accessed on instances.

For more details, see the typing spec on ClassVar.

from typing import ClassVar

class C:
    pure_class_variable1: ClassVar[str] = "value in class body"
    pure_class_variable2: ClassVar = 1

    def method(self):
        # TODO: this should be an error
        self.pure_class_variable1 = "value set through instance"

reveal_type(C.pure_class_variable1)  # revealed: str

# TODO: Should be `Unknown | Literal[1]`.
reveal_type(C.pure_class_variable2)  # revealed: Unknown

c_instance = C()

# It is okay to access a pure class variable on an instance.
reveal_type(c_instance.pure_class_variable1)  # revealed: str

# TODO: Should be `Unknown | Literal[1]`.
reveal_type(c_instance.pure_class_variable2)  # revealed: Unknown

# error: [invalid-attribute-access] "Cannot assign to ClassVar `pure_class_variable1` from an instance of type `C`"
c_instance.pure_class_variable1 = "value set on instance"

C.pure_class_variable1 = "overwritten on class"

# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `pure_class_variable1` of type `str`"
C.pure_class_variable1 = 1

class Subclass(C):
    pure_class_variable1: ClassVar[str] = "overwritten on subclass"

reveal_type(Subclass.pure_class_variable1)  # revealed: str

Variable only mentioned in a class method

We also consider a class variable to be a pure class variable if it is only mentioned in a class method.

class C:
    @classmethod
    def class_method(cls):
        cls.pure_class_variable = "value set in class method"

# for a more realistic example, let's actually call the method
C.class_method()

# TODO: We currently plan to support this and show no error here.
# mypy shows an error here, pyright does not.
# error: [unresolved-attribute]
reveal_type(C.pure_class_variable)  # revealed: Unknown

C.pure_class_variable = "overwritten on class"

# TODO: should be  `Unknown | Literal["value set in class method"]` or
# Literal["overwritten on class"]`, once/if we support local narrowing.
# error: [unresolved-attribute]
reveal_type(C.pure_class_variable)  # revealed: Unknown

c_instance = C()
reveal_type(c_instance.pure_class_variable)  # revealed: Unknown | Literal["value set in class method"]

# TODO: should raise an error.
c_instance.pure_class_variable = "value set on instance"

Instance variables with class-level default values

These are instance attributes, but the fact that we can see that they have a binding (not a declaration) in the class body means that reading the value from the class directly is also permitted. This is the only difference for these attributes as opposed to "pure" instance attributes.

Basic

class C:
    variable_with_class_default1: str = "value in class body"
    variable_with_class_default2 = 1

    def instance_method(self):
        self.variable_with_class_default1 = "value set in instance method"

reveal_type(C.variable_with_class_default1)  # revealed: str

reveal_type(C.variable_with_class_default2)  # revealed: Unknown | Literal[1]

c_instance = C()

reveal_type(c_instance.variable_with_class_default1)  # revealed: str
reveal_type(c_instance.variable_with_class_default2)  # revealed: Unknown | Literal[1]

c_instance.variable_with_class_default1 = "value set on instance"

reveal_type(C.variable_with_class_default1)  # revealed: str

# TODO: Could be Literal["value set on instance"], or still `str` if we choose not to
# narrow the type.
reveal_type(c_instance.variable_with_class_default1)  # revealed: str

C.variable_with_class_default1 = "overwritten on class"

# TODO: Could be `Literal["overwritten on class"]`, or still `str` if we choose not to
# narrow the type.
reveal_type(C.variable_with_class_default1)  # revealed: str

# TODO: should still be `Literal["value set on instance"]`, or `str`.
reveal_type(c_instance.variable_with_class_default1)  # revealed: str

Inheritance of class/instance attributes

Instance variable defined in a base class

class Base:
    declared_in_body: int | None = 1

    base_class_attribute_1: str | None
    base_class_attribute_2: str | None
    base_class_attribute_3: str | None

    def __init__(self) -> None:
        self.defined_in_init: str | None = "value in base"

class Intermediate(Base):
    # Re-declaring base class attributes with the *same *type is fine:
    base_class_attribute_1: str | None = None

    # Re-declaring them with a *narrower type* is unsound, because modifications
    # through a `Base` reference could violate that constraint.
    #
    # Mypy does not report an error here, but pyright does: "… overrides symbol
    # of same name in class "Base". Variable is mutable so its type is invariant"
    #
    # We should introduce a diagnostic for this. Whether or not that should be
    # enabled by default can still be discussed.
    #
    # TODO: This should be an error
    base_class_attribute_2: str

    # Re-declaring attributes with a *wider type* directly violates LSP.
    #
    # In this case, both mypy and pyright report an error.
    #
    # TODO: This should be an error
    base_class_attribute_3: str | int | None

class Derived(Intermediate): ...

reveal_type(Derived.declared_in_body)  # revealed: int | None

reveal_type(Derived().declared_in_body)  # revealed: int | None

reveal_type(Derived().defined_in_init)  # revealed: str | None

Union of attributes

def _(flag: bool):
    if flag:
        class C1:
            x = 1

    else:
        class C1:
            x = 2

    class C2:
        if flag:
            x = 3
        else:
            x = 4

    reveal_type(C1.x)  # revealed: Unknown | Literal[1, 2]
    reveal_type(C2.x)  # revealed: Unknown | Literal[3, 4]

Inherited class attributes

Basic

class A:
    X = "foo"

class B(A): ...
class C(B): ...

reveal_type(C.X)  # revealed: Unknown | Literal["foo"]

Multiple inheritance

class O: ...

class F(O):
    X = 56

class E(O):
    X = 42

class D(O): ...
class C(D, F): ...
class B(E, D): ...
class A(B, C): ...

# revealed: tuple[Literal[A], Literal[B], Literal[E], Literal[C], Literal[D], Literal[F], Literal[O], Literal[object]]
reveal_type(A.__mro__)

# `E` is earlier in the MRO than `F`, so we should use the type of `E.X`
reveal_type(A.X)  # revealed: Unknown | Literal[42]

Unions with possibly unbound paths

Definite boundness within a class

In this example, the x attribute is not defined in the C2 element of the union:

def _(flag1: bool, flag2: bool):
    class C1:
        x = 1

    class C2: ...

    class C3:
        x = 3

    C = C1 if flag1 else C2 if flag2 else C3

    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
    reveal_type(C.x)  # revealed: Unknown | Literal[1, 3]

Possibly-unbound within a class

We raise the same diagnostic if the attribute is possibly-unbound in at least one element of the union:

def _(flag: bool, flag1: bool, flag2: bool):
    class C1:
        x = 1

    class C2:
        if flag:
            x = 2

    class C3:
        x = 3

    C = C1 if flag1 else C2 if flag2 else C3

    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
    reveal_type(C.x)  # revealed: Unknown | Literal[1, 2, 3]

Unions with all paths unbound

If the symbol is unbound in all elements of the union, we detect that:

def _(flag: bool):
    class C1: ...
    class C2: ...
    C = C1 if flag else C2

    # error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
    reveal_type(C.x)  # revealed: Unknown

Objects of all types have a `class` method

import typing_extensions

reveal_type(typing_extensions.__class__)  # revealed: Literal[ModuleType]

a = 42
reveal_type(a.__class__)  # revealed: Literal[int]

b = "42"
reveal_type(b.__class__)  # revealed: Literal[str]

c = b"42"
reveal_type(c.__class__)  # revealed: Literal[bytes]

d = True
reveal_type(d.__class__)  # revealed: Literal[bool]

e = (42, 42)
reveal_type(e.__class__)  # revealed: Literal[tuple]

def f(a: int, b: typing_extensions.LiteralString, c: int | str, d: type[str]):
    reveal_type(a.__class__)  # revealed: type[int]
    reveal_type(b.__class__)  # revealed: Literal[str]
    reveal_type(c.__class__)  # revealed: type[int] | type[str]

    # `type[type]`, a.k.a., either the class `type` or some subclass of `type`.
    # It would be incorrect to infer `Literal[type]` here,
    # as `c` could be some subclass of `str` with a custom metaclass.
    # All we know is that the metaclass must be a (non-strict) subclass of `type`.
    reveal_type(d.__class__)  # revealed: type[type]

reveal_type(f.__class__)  # revealed: Literal[FunctionType]

class Foo: ...

reveal_type(Foo.__class__)  # revealed: Literal[type]

Module attributes

mod.py:

global_symbol: str = "a"

import mod

reveal_type(mod.global_symbol)  # revealed: str
mod.global_symbol = "b"

# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `global_symbol` of type `str`"
mod.global_symbol = 1

# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `global_symbol` of type `str`"
(_, mod.global_symbol) = (..., 1)

# TODO: this should be an error, but we do not understand list unpackings yet.
[_, mod.global_symbol] = [1, 2]

class IntIterator:
    def __next__(self) -> int:
        return 42

class IntIterable:
    def __iter__(self) -> IntIterator:
        return IntIterator()

# error: [invalid-assignment] "Object of type `int` is not assignable to attribute `global_symbol` of type `str`"
for mod.global_symbol in IntIterable():
    pass

Nested attributes

outer/__init__.py:

outer/nested/__init__.py:

outer/nested/inner.py:

class Outer:
    class Nested:
        class Inner:
            attr: int = 1

import outer.nested.inner

reveal_type(outer.nested.inner.Outer.Nested.Inner.attr)  # revealed: int

# error: [invalid-assignment]
outer.nested.inner.Outer.Nested.Inner.attr = "a"

Literal types

Function-literal attributes

Most attribute accesses on function-literal types are delegated to types.FunctionType, since all functions are instances of that class:

a.py:

def f(): ...

reveal_type(f.__defaults__)  # revealed: @Todo(full tuple[...] support) | None
reveal_type(f.__kwdefaults__)  # revealed: @Todo(generics) | None

Some attributes are special-cased, however:

b.py:

def f(): ...

reveal_type(f.__get__)  # revealed: @Todo(`__get__` method on functions)
reveal_type(f.__call__)  # revealed: @Todo(`__call__` method on functions)

Int-literal attributes

Most attribute accesses on int-literal types are delegated to builtins.int, since all literal integers are instances of that class:

a.py:

reveal_type((2).bit_length)  # revealed: @Todo(bound method)
reveal_type((2).denominator)  # revealed: @Todo(@property)

Some attributes are special-cased, however:

b.py:

reveal_type((2).numerator)  # revealed: Literal[2]
reveal_type((2).real)  # revealed: Literal[2]

Bool-literal attributes

Most attribute accesses on bool-literal types are delegated to builtins.bool, since all literal bols are instances of that class:

a.py:

reveal_type(True.__and__)  # revealed: @Todo(bound method)
reveal_type(False.__or__)  # revealed: @Todo(bound method)

Some attributes are special-cased, however:

b.py:

reveal_type(True.numerator)  # revealed: Literal[1]
reveal_type(False.real)  # revealed: Literal[0]

Bytes-literal attributes

All attribute access on literal bytes types is currently delegated to buitins.bytes:

reveal_type(b"foo".join)  # revealed: @Todo(bound method)
reveal_type(b"foo".endswith)  # revealed: @Todo(bound method)

Instance attribute edge cases

Assignment to attribute that does not correspond to the instance

class Other:
    x: int = 1

class C:
    def __init__(self, other: Other) -> None:
        other.x = 1

def f(c: C):
    # error: [unresolved-attribute]
    reveal_type(c.x)  # revealed: Unknown

Nested classes

class Outer:
    def __init__(self):
        self.x: int = 1

    class Middle:
        # has no 'x' attribute

        class Inner:
            def __init__(self):
                self.x: str = "a"

reveal_type(Outer().x)  # revealed: int

# error: [unresolved-attribute]
Outer.Middle().x

reveal_type(Outer.Middle.Inner().x)  # revealed: str

Shadowing of `self`

class Other:
    x: int = 1

class C:
    def __init__(self) -> None:
        # Redeclaration of self. `self` does not refer to the instance anymore.
        self: Other = Other()
        self.x: int = 1

# TODO: this should be an error
C().x

Assignment to `self` after nested function

class Other:
    x: str = "a"

class C:
    def __init__(self) -> None:
        def nested_function(self: Other):
            self.x = "b"
        self.x: int = 1

reveal_type(C().x)  # revealed: int

Assignment to `self` from nested function

class C:
    def __init__(self) -> None:
        def set_attribute(value: str):
            self.x: str = value
        set_attribute("a")

# TODO: ideally, this would be `str`. Mypy supports this, pyright does not.
# error: [unresolved-attribute]
reveal_type(C().x)  # revealed: Unknown

References

Some of the tests in the Class and instance variables section draw inspiration from pyright's documentation on this topic.

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Attributes

Class and instance variables

Pure instance variables

Variable only declared/bound in __init__

Variable declared in class body and possibly bound in __init__

Variable declared in class body and not bound anywhere

Mixed declarations/bindings in class body and __init__

Variable defined in non-__init__ method

Variable defined in multiple methods

Attributes defined in tuple unpackings

Attributes defined in for-loop (unpacking)

Conditionally declared / bound attributes

Methods that does not use self as a first parameter

Aliased self parameter

Static methods do not influence implicitly defined attributes

Attributes defined in statically-known-to-be-false branches

Pure class variables (ClassVar)

Annotated with ClassVar type qualifier

Variable only mentioned in a class method

Instance variables with class-level default values

Basic

Inheritance of class/instance attributes

Instance variable defined in a base class

Union of attributes

Inherited class attributes

Basic

Multiple inheritance

Unions with possibly unbound paths

Definite boundness within a class

Possibly-unbound within a class

Unions with all paths unbound

Objects of all types have a __class__ method

Module attributes

Nested attributes

Literal types

Function-literal attributes

Int-literal attributes

Bool-literal attributes

Bytes-literal attributes

Instance attribute edge cases

Assignment to attribute that does not correspond to the instance

Nested classes

Shadowing of self

Assignment to self after nested function

Assignment to self from nested function

References

Variable only declared/bound in `init`

Variable declared in class body and possibly bound in `init`

Mixed declarations/bindings in class body and `init`

Variable defined in non-`init` method

Methods that does not use `self` as a first parameter

Aliased `self` parameter

Pure class variables (`ClassVar`)

Annotated with `ClassVar` type qualifier

Objects of all types have a `class` method

Shadowing of `self`

Assignment to `self` after nested function

Assignment to `self` from nested function