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feat: add typing.Self #5710

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feat: add typing.Self #5710

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feat: add typing.Self 
Signed-off-by: Nick Mitchell <[email protected]>
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@starpit
starpit committed Apr 19, 2025
commit 05b58dbae9d222c25a5d88c9edd87b3955c6871b
22 changes: 21 additions & 1 deletion Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,7 @@
'ParamSpecArgs',
'ParamSpecKwargs',
'runtime_checkable',
'Self',
'Text',
'TYPE_CHECKING',
'TypeAlias',
Expand Down Expand Up @@ -164,7 +165,7 @@ def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=
if (isinstance(arg, _GenericAlias) and
arg.__origin__ in invalid_generic_forms):
raise TypeError(f"{arg} is not valid as type argument")
if arg in (Any, NoReturn, Final, TypeAlias):
if arg in (Any, NoReturn, Final, Self, TypeAlias):
return arg
if isinstance(arg, _SpecialForm) or arg in (Generic, Protocol):
raise TypeError(f"Plain {arg} is not valid as type argument")
Expand Down Expand Up @@ -438,6 +439,25 @@ def stop() -> NoReturn:
"""
raise TypeError(f"{self} is not subscriptable")

@_SpecialForm
def Self(self, parameters):
"""Used to spell the type of "self" in classes.

Example::

from typing import Self

class Foo:
def return_self(self) -> Self:
...
return self

This is especially useful for:
- classmethods that are used as alternative constructors
- annotating an `__enter__` method which returns self
"""
raise TypeError(f"{self} is not subscriptable")

@_SpecialForm
def ClassVar(self, parameters):
"""Special type construct to mark class variables.
Expand Down
8 changes: 8 additions & 0 deletions extra_tests/snippets/stdlib_typing.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
from typing import Self

class Shape:
def set_scale(self, scale: float) -> Self:
self.scale = scale
return self

print(Shape().set_scale(3).scale)
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