gh-118013: Use weakrefs for the cache key in inspect._shadowed_dict

[AlexWaygood]

Slower than main, but significantly faster than a straight revert of #104267.

• Issue: [3.12] getattr_static can result in reference leaks #118013

[carljm]

Looks good to me, once we get news/tests/benchmarks.

[AlexWaygood]

Benchmarks

All timings done with a fresh PGO-optimised build on main using a MacBook pro.

getattr_static benchmarks:

Benchmark script

fromtimeitimporttimeitfromstatisticsimportmean, stdevfrominspectimportgetattr_staticclassFoo:
@propertydefx(self) ->int:
return42classBar:
x=42classWithParentClassX(Bar): ...
classBaz:
def__init__(self):
self.x=42classWithParentX(Baz): ...
classMissing: ...
classSlotted:
__slots__= ('x',)
def__init__(self):
self.x=42classMethod:
defx(self): ...
classClsMethod:
@classmethoddefx(cls): ...
classStMethod:
@staticmethoddefx(): ...
importgcgc.disable()
times= []
defstats():
ts= [t*1e8fortinsorted(times)[:5]]
returnf'{round(mean(ts)):4} ± {round(stdev(ts)):2} ns 'defbench(obj):
# Warmup:for_inrange(5):
number=100timeit(lambda: getattr_static(obj, 'x', None), number=number)
# Actual bench:for_inrange(50):
number=1000t=timeit(lambda: getattr_static(obj, 'x', None), number=number) /numbertimes.append(t)
bench_name= (
f'type[{obj.__name__}]'ifisinstance(obj, type)
elseobj.__class__.__name__
)
print(f"{bench_name: <25}: {stats()}")
times.clear()
bench(Foo)
bench(Foo())
bench(Bar)
bench(Bar())
bench(WithParentClassX())
bench(Baz())
bench(WithParentX())
bench(Missing)
bench(Missing())
bench(Slotted())
bench(Method())
bench(StMethod())
bench(ClsMethod())

Results on main

type[Foo] : 26 ± 1 ns Foo : 44 ± 0 ns type[Bar] : 26 ± 0 ns Bar : 40 ± 0 ns WithParentClassX : 52 ± 0 ns Baz : 49 ± 0 ns WithParentX : 59 ± 0 ns type[Missing] : 56 ± 0 ns Missing : 50 ± 0 ns Slotted : 57 ± 0 ns Method : 39 ± 0 ns StMethod : 39 ± 0 ns ClsMethod : 39 ± 0 ns

Results with this PR

type[Foo] : 39 ± 0 ns Foo : 60 ± 1 ns type[Bar] : 33 ± 0 ns Bar : 56 ± 0 ns WithParentClassX : 79 ± 0 ns Baz : 72 ± 0 ns WithParentX : 92 ± 0 ns type[Missing] : 86 ± 0 ns Missing : 74 ± 0 ns Slotted : 74 ± 0 ns Method : 56 ± 0 ns StMethod : 56 ± 0 ns ClsMethod : 56 ± 0 ns

Results with a clean revert of #104267

type[Foo] : 43 ± 0 ns Foo : 66 ± 1 ns type[Bar] : 37 ± 0 ns Bar : 65 ± 0 ns WithParentClassX : 91 ± 0 ns Baz : 84 ± 0 ns WithParentX : 111 ± 0 ns type[Missing] : 103 ± 0 ns Missing : 85 ± 0 ns Slotted : 78 ± 0 ns Method : 65 ± 0 ns StMethod : 65 ± 0 ns ClsMethod : 65 ± 0 ns

Runtime-checkable protocol benchmarks

Benchmark script

fromtypingimportProtocol, runtime_checkable@runtime_checkableclassFoo(Protocol):
a: intb: intc: intd: inte: intf: intg: inth: inti: intj: intk: intl: intm: intn: into: intp: intq: intr: ints: intt: intu: intv: intw: intx: inty: intz: intclassBar:
def__init__(self):
forattrnamein'abcdefghijklmnopqrstuvwxyz':
setattr(self, attrname, 42)
bars= [Bar() for_inrange(100_000)]
importtimestart=time.perf_counter()
forbarinbars:
isinstance(bar, Foo)
print(time.perf_counter() -start)

Results on main: 1.3446190829854459

Results with this PR: 1.9680303339846432

Results with a clean revert of #104267: 2.243281374918297

[AlexWaygood]

(The getattr_static() benchmark script was originally contributed by @sobolevn in #103193 (comment))

[carljm]

🎉

[miss-islington-app]

Thanks @AlexWaygood for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-118232 is a backport of this pull request to the 3.12 branch.