gh-103193: Micro-optimise helper functions for `inspect.getattr_static` by AlexWaygood · Pull Request #103195 · python/cpython · GitHub

Micro-optimising inspect._static_getmro and inspect._shadowed_dict leads to a significant improvement in the time taken to call isinstance() on a runtime-checkable protocol. (This is a useful benchmark, as it's a real-world use of inspect.getattr_static in a tight loop, that's found in the stdlib.)

Benchmark results on a0305c5:

Time taken for objects with a property: 3.34
Time taken for objects with a classvar: 3.08
Time taken for objects with an instance var: 12.15
Time taken for objects with no var: 15.38
Time taken for nominal subclass instances: 25.13
Time taken for registered subclass instances: 21.65

Benchmark results with this PR:

Time taken for objects with a property: 2.82
Time taken for objects with a classvar: 2.85
Time taken for objects with an instance var: 8.62
Time taken for objects with no var: 14.01
Time taken for nominal subclass instances: 21.80
Time taken for registered subclass instances: 20.23

Benchmark script:

import time
from typing import Protocol, runtime_checkable

@runtime_checkable
class HasX(Protocol):
    x: int

class Foo:
    @property
    def x(self) -> int:
        return 42

class Bar:
    x = 42

class Baz:
    def __init__(self):
        self.x = 42

class Egg: ...

class Nominal(HasX):
    def __init__(self):
        self.x = 42

class Registered: ...

HasX.register(Registered)

num_instances = 500_000
foos = [Foo() for _ in range(num_instances)]
bars = [Bar() for _ in range(num_instances)]
bazzes = [Baz() for _ in range(num_instances)]
basket = [Egg() for _ in range(num_instances)]
nominals = [Nominal() for _ in range(num_instances)]
registereds = [Registered() for _ in range(num_instances)]


def bench(objs, title):
    start_time = time.perf_counter()
    for obj in objs:
        isinstance(obj, HasX)
    elapsed = time.perf_counter() - start_time
    print(f"{title}: {elapsed:.2f}")


bench(foos, "Time taken for objects with a property")
bench(bars, "Time taken for objects with a classvar")
bench(bazzes, "Time taken for objects with an instance var")
bench(basket, "Time taken for objects with no var")
bench(nominals, "Time taken for nominal subclass instances")
bench(registereds, "Time taken for registered subclass instances")

Issue: Optimise inspect.getattr_static #103193

…_static`

I can find one significant bug report open regarding inspect.getattr_static:

Fix data descriptor detection in inspect.getattr_static #75367

Having studied the bug report, I don't think this patch impacts the bug (or any possible solutions to the bug) either way.

Hello, Alex!
Just out of curiosity, why do you use a x.__dict__ instead of vars(x), it's related to a performance issues?

Just out of curiosity, why do you use a x.__dict__ instead of vars(x), it's related to a performance issues?

There's not really any difference between the two; it's just a matter of taste. Some people consider vars(x) to be "more Pythonic" than accessing the __dict__ variable directly, but I don't really have a strong preference either way.

In this case, the main reason I'm accessing it via .__dict__ is just because that's what the existing code already does, and I don't see any reason to change the style here. It's also arguably more explicit in this case -- but again, that's just a subjective opinion about code readability, really.

There are several things I can think of to speed up getattr_static.

Change _check_instance to be

def _check_instance(obj, attr):
    try:
        instance_dict = object.__getattribute__(obj, "__dict__")
    except AttributeError:
        return _sentinel
    return dict.get(instance_dict, attr, _sentinel)

Here type is called twice:

if (_check_class(type(klass_result), '__get__') is not _sentinel and
            _check_class(type(klass_result), '__set__') is not _sentinel):

Ideally we can also call _check_class once with several attributes 🤔
Because in this case it will allow us to decrease the amount of _static_mro calls.

I think that a variable might be a bit faster

There are several things I can think of to speed up getattr_static.

Those sound great! My instinct is to tackle them in a separate PR, so that each change can be evaluated and benchmarked independently. Would you like to submit a PR?

Yes, I will do it tomorrow 👍

Would it be ok to have _dunder_dict_descriptor_get = type.__dict__["__dict__"].__get__ instead of _dunder_dict_descriptor = type.__dict__["__dict__"] in order to minimize the number of accesses to __get__ when iterating over the classes ?

Would it be ok to have _dunder_dict_descriptor_get = type.__dict__["__dict__"].__get__ instead of _dunder_dict_descriptor = type.__dict__["__dict__"] in order to minimize the number of accesses to __get__ when iterating over the classes ?

I considered it, but felt like it would make it significantly less readable (_dunder_dict_descriptor already isn't a great name, and _dunder_dict_descriptor_get feels even worse). Happy to reconsider if others agree that we should go that way, though.

_dunder_dict_descriptor already isn't a great name, and _dunder_dict_descriptor_get feels even worse

IMO, since we are already micro-optimizing an internal helper of an internal function, we may not necessarily need to be exact so perhaps we can name it _dunder_dict_of ?

IMO, since we are already micro-optimizing an internal helper of an internal function, we may not necessarily need to be exact so perhaps we can name it _dunder_dict_of ?

That's a decent name. Or maybe _get_dunder_dict_of_class.

I'll make the change — thanks!

I pushed the change and updated the benchmark results in the PR description (it's maybe a teeny tiny bit faster than it was, but not by much)

it's maybe a teeny tiny bit faster than it was, but not by much

I think the impact will be clearer when we have a complicated inheritance diagram (e.g., large projects with abstract interfaces and/or mixins here and there).

Very nice!

There are several things I can think of to speed up getattr_static.

Change _check_instance to be
def _check_instance(obj, attr):
    try:
        instance_dict = object.__getattribute__(obj, "__dict__")
    except AttributeError:
        return _sentinel
    return dict.get(instance_dict, attr, _sentinel)
Here type is called twice:
if (_check_class(type(klass_result), '__get__') is not _sentinel and
            _check_class(type(klass_result), '__set__') is not _sentinel):
Ideally we can also call _check_class once with several attributes 🤔 Because in this case it will allow us to decrease the amount of _static_mro calls.

I think that a variable might be a bit faster

I tried these out locally, but unfortunately I can't measure any speedup from them :/

It's possible I'm not using the right benchmark to show a speedup, however -- happy to be proven wrong if you can get a speedup somewhere!

…_static` (python#103195)

pythongh-103193 : Micro-optimise helper functions for `inspect.getattr…

469e165

…_static`

AlexWaygood added type-feature A feature request or enhancement performance Performance or resource usage stdlib Standard Library Python modules in the Lib/ directory 3.12 only security fixes labels Apr 2, 2023

AlexWaygood requested a review from carljm April 2, 2023 17:05

bedevere-bot added the awaiting core review label Apr 2, 2023

bedevere-bot mentioned this pull request Apr 2, 2023

Optimise inspect.getattr_static #103193

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sobolevn reviewed Apr 3, 2023

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carljm approved these changes Apr 5, 2023

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bedevere-bot added awaiting merge and removed awaiting core review labels Apr 5, 2023

AlexWaygood merged commit 264c00a into python:main Apr 5, 2023

bedevere-bot removed the awaiting merge label Apr 5, 2023

AlexWaygood deleted the microoptimise-getattr_static-helpers branch April 5, 2023 07:27

This was referenced Apr 6, 2023

gh-103193: Use LBYL idioms rather than EAFP in inspect.getattr_static #103318

Merged

gh-74690: Document changes made to runtime-checkable protocols in 3.12 #103348

Merged

gaogaotiantian pushed a commit to gaogaotiantian/cpython that referenced this pull request Apr 8, 2023

pythongh-103193 : Micro-optimise helper functions for `inspect.getattr…

62d4471

…_static` (python#103195)

warsaw pushed a commit to warsaw/cpython that referenced this pull request Apr 11, 2023

pythongh-103193 : Micro-optimise helper functions for `inspect.getattr…

55c701e

…_static` (python#103195)

gh-103193: Micro-optimise helper functions for `inspect.getattr_static` by AlexWaygood · Pull Request #103195 · python/cpython · GitHub

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gh-103193: Micro-optimise helper functions for inspect.getattr_static - #103195

gh-103193: Micro-optimise helper functions for inspect.getattr_static#103195AlexWaygood merged 2 commits intopython:mainpython/cpython:mainfrom AlexWaygood:microoptimise-getattr_static-helpersAlexWaygood/cpython:microoptimise-getattr_static-helpersCopy head branch name to clipboard

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gh-103193: Micro-optimise helper functions for inspect.getattr_static#103195
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