gh-103193: Use LBYL idioms rather than EAFP in inspect.getattr_static

[AlexWaygood]

This PR significantly speeds up inspect.getattr_static() and, as a result, isinstance() checks against runtime-checkable protocols.

Here are benchmark results on main using @sobolevn's benchmark script from #103193 (comment):

type[Foo] : 89 ± 0 ns
Foo : 212 ± 0 ns
type[Bar] : 90 ± 0 ns
Bar : 213 ± 0 ns
WithParentClassX : 331 ± 0 ns
Baz : 325 ± 1 ns
WithParentX : 441 ± 1 ns
type[Missing] : 422 ± 1 ns
Missing : 328 ± 1 ns
Slotted : 267 ± 0 ns
Method : 213 ± 0 ns
StMethod : 214 ± 0 ns
ClsMethod : 213 ± 0 ns

And here are the benchmark results with this PR:

type[Foo] : 75 ± 0 ns
Foo : 179 ± 0 ns
type[Bar] : 75 ± 0 ns
Bar : 179 ± 0 ns
WithParentClassX : 232 ± 1 ns
Baz : 216 ± 0 ns
WithParentX : 265 ± 0 ns
type[Missing] : 209 ± 0 ns
Missing : 218 ± 0 ns
Slotted : 214 ± 0 ns
Method : 178 ± 0 ns
StMethod : 178 ± 0 ns
ClsMethod : 178 ± 0 ns

A result of this optimisation is that the following isinstance() call becomes around 1.5x faster:

fromtypingimport*@runtime_checkableclassFoo(Protocol):
a: intb: intc: intd: inte: intf: intg: inth: inti: intj: intclassBar:
def__init__(self):
forattrnamein'abcdefghij':
setattr(self, attrname, 42)
isinstance(Bar(), Foo)

• Issue: Optimise inspect.getattr_static #103193

[AlexWaygood]

Skipping news, since the news entry in #103195 should suffice, I think.

[carljm]

It's less idiomatic code, but I think it's worth it for the very significant performance improvement on runtime protocol isinstance checking with many attributes.

I assume you've checked the performance of using .get(...) and it's worse?

[AlexWaygood]

I assume you've checked the performance of using .get(...) and it's worse?

Hmm I haven't, actually -- not sure how you'd use .get() here in an idiomatic way? Can you show me what you mean?

[AlexWaygood]

Oh I think I see what you mean. Trying it out now.

[AlexWaygood]

Yeah, I tried out doing this instead (diff is relative to my current patch, not to main), and it's slower than what I currently have:

diff --git a/Lib/inspect.py b/Lib/inspect.py
index a317f0ca74..7fcaa13750 100644
--- a/Lib/inspect.py+++ b/Lib/inspect.py@@ -1787,8 +1787,10 @@ def _check_instance(obj, attr):
def _check_class(klass, attr):
for entry in _static_getmro(klass):
- if _shadowed_dict(type(entry)) is _sentinel and attr in entry.__dict__:- return entry.__dict__[attr]+ if _shadowed_dict(type(entry)) is _sentinel:+ ret = entry.__dict__.get(attr, _sentinel)+ if ret is not _sentinel:+ return ret
return _sentinel
def _is_type(obj):
@@ -1800,13 +1802,13 @@ def _is_type(obj):
def _shadowed_dict(klass):
for entry in _static_getmro(klass):
- dunder_dict = _get_dunder_dict_of_class(entry)- if '__dict__' in dunder_dict:- class_dict = dunder_dict['__dict__']- if not (type(class_dict) is types.GetSetDescriptorType and- class_dict.__name__ == "__dict__" and- class_dict.__objclass__ is entry):- return class_dict+ class_dict = _get_dunder_dict_of_class(entry).get('__dict__', _sentinel)+ if class_dict is not _sentinel and not (+ type(class_dict) is types.GetSetDescriptorType+ and class_dict.__name__ == "__dict__"+ and class_dict.__objclass__ is entry+ ):+ return class_dict
return _sentinel
def getattr_static(obj, attr, default=_sentinel):
@@ -1845,11 +1847,10 @@ def getattr_static(obj, attr, default=_sentinel):
if obj is klass:
# for types we check the metaclass too
for entry in _static_getmro(type(klass)):
- if (- _shadowed_dict(type(entry)) is _sentinel- and attr in entry.__dict__- ):- return entry.__dict__[attr]+ if _shadowed_dict(type(entry)) is _sentinel:+ ret = entry.__dict__.get(attr, _sentinel)+ if ret is not _sentinel:+ return ret

@carljm is that the kind of thing you were talking about? :)

[sobolevn]

Good idea!

[AlexWaygood]

Thanks both!