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gh-130827: Support typing.Self annotations in singledispatchmethod() #130829

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gh-130827: Support typing.Self annotations in singledispatchmethod() #130829

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d466dc4
gh-130827: Support typing.Self in singledispatchmethod()
ZeroIntensity Mar 4, 2025
fd7e374
Add blurb.
ZeroIntensity Mar 4, 2025
2e6b46f
Update Lib/test/test_functools.py
ZeroIntensity Mar 4, 2025
f571ec7
Update Lib/functools.py
ZeroIntensity Mar 4, 2025
658d3fe
Add some checks for edge cases.
ZeroIntensity Mar 17, 2025
2558b74
Fix code written with stupid nano.
ZeroIntensity Mar 17, 2025
f61d8a4
Fix indentation in comment.
ZeroIntensity Apr 2, 2025
65a9a95
Merge branch 'main' into typing-self-singledispatch
ZeroIntensity Apr 14, 2025
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gh-130827: Support typing.Self in singledispatchmethod()
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@ZeroIntensity
ZeroIntensity committed Mar 4, 2025
commit d466dc40472da6f4e14e66493375a8c0674b10ab
36 changes: 24 additions & 12 deletions 36 Lib/functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -885,15 +885,7 @@ def _find_impl(cls, registry):
match = t
return registry.get(match)

def singledispatch(func):
"""Single-dispatch generic function decorator.

Transforms a function into a generic function, which can have different
behaviours depending upon the type of its first argument. The decorated
function acts as the default implementation, and additional
implementations can be registered using the register() attribute of the
generic function.
"""
def _singledispatchimpl(func, is_method):
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# There are many programs that use functools without singledispatch, so we
# trade-off making singledispatch marginally slower for the benefit of
# making start-up of such applications slightly faster.
Expand Down Expand Up @@ -963,9 +955,19 @@ def register(cls, func=None):
func = cls

# only import typing if annotation parsing is necessary
from typing import get_type_hints
from typing import get_type_hints, Self
from annotationlib import Format, ForwardRef
argname, cls = next(iter(get_type_hints(func, format=Format.FORWARDREF).items()))
hints_iter = iter(get_type_hints(func, format=Format.FORWARDREF).items())
argname, cls = next(hints_iter)
if cls is Self:
if not is_method:
raise TypeError(
f"Invalid annotation for {argname!r}. ",
"typing.Self can only be used with singledispatchmethod()"
)
else:
argname, cls = next(hints_iter)
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if not _is_valid_dispatch_type(cls):
if _is_union_type(cls):
raise TypeError(
Expand Down Expand Up @@ -1010,6 +1012,16 @@ def wrapper(*args, **kw):
update_wrapper(wrapper, func)
return wrapper

def singledispatch(func):
"""Single-dispatch generic function decorator.

Transforms a function into a generic function, which can have different
behaviours depending upon the type of its first argument. The decorated
function acts as the default implementation, and additional
implementations can be registered using the register() attribute of the
generic function.
"""
return _singledispatchimpl(func, is_method=False)

# Descriptor version
class singledispatchmethod:
Expand All @@ -1023,7 +1035,7 @@ def __init__(self, func):
if not callable(func) and not hasattr(func, "__get__"):
raise TypeError(f"{func!r} is not callable or a descriptor")

self.dispatcher = singledispatch(func)
self.dispatcher = _singledispatchimpl(func, is_method=True)
self.func = func

def register(self, cls, method=None):
Expand Down
24 changes: 24 additions & 0 deletions 24 Lib/test/test_functools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3362,6 +3362,30 @@ def _(item, arg: bytes) -> str:
self.assertEqual(str(Signature.from_callable(A.static_func)),
'(item, arg: int) -> str')

def test_typing_self(self):
# gh-130827: typing.Self with singledispatchmethod() didn't work
class Foo:
@functools.singledispatchmethod
def bar(self: typing.Self, arg: int | str) -> int | str: ...

@bar.register
def _(self: typing.Self, arg: int) -> int:
return arg


foo = Foo()
self.assertEqual(foo.bar(42), 42)

@functools.singledispatch
def test(self: typing.Self, arg: int | str) -> int | str:
pass
# But, it shouldn't work on singledispatch()
with self.assertRaises(TypeError):
@test.register
def silly(self: typing.Self, arg: int | str) -> int | str:
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Will 'typing.Self' annotation work the same way?

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Good question! It should, yeah. get_type_hints handles forward references.

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Should we add a test case for that, maybe?

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Possibly, but as long as get_type_hints is working it's probably fine.

pass

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class CachedCostItem:
_cost = 1
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