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Performance of typing._ProtocolMeta._get_protocol_attrs and isinstance #74690Description
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assignee = None
closed_at = None
created_at = <Date 2017-05-29.09:16:49.884>
labels = ['library', 'performance']
title = 'Performance of typing._ProtocolMeta._get_protocol_attrs and isinstance'
updated_at = <Date 2017-06-02.17:44:59.311>
user = 'https://github.com/orenbenkiki' bugs.python.org fields:
activity = <Date 2017-06-02.17:44:59.311>
actor = 'levkivskyi'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-05-29.09:16:49.884>
creator = 'orenbenkiki'
dependencies = []
files = []
hgrepos = []
issue_num = 30505
keywords = []
message_count = 2.0
messages = ['294686', '295044']
nosy_count = 2.0
nosy_names = ['levkivskyi', 'orenbenkiki']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue30505'
versions = ['Python 3.6'] Linked PRs
Activityorenbenkiki commented on May 29, 2017 MannequinAuthor More actions In 3.6.0, invocation of isinstance calls typing._ProtocolMeta._get_protocol_attrs.
This creates a set of all attributes in all base classes, loops on these attributes to check they exist, and discards the set. It is very slow.
My program uses isinstance to allow for flexibility in parameter types in certain key functions. I realize that using isinstance is frowned upon, but it seems to make sense in my case.
As a result, >95% of its run-time is inside typing._ProtocolMeta._get_protocol_attrs (!).
I have created a simple wrapper around isinstance which caches its result with a Dict[Tuple[type, type], bool]. This solved the performance problem, but introduced a different problem - type checking.
I use mypy and type annotations, and my code cleanly type-checks (with the occasional # type: ignore). If I switch to using my own isinstance function, then mypy's type inference no longer treats it as special, so it starts complaining about all uses of values protected by if isinstance(value, SomeType): ...
I propose that either the private typing._ProtocolMeta.__subclasscheck__ (which invokes _get_protocol_attrs), or the public isinstance, would be modified to cache their results.
I can create a PR for either approach, if this is acceptable. ilevkivskyi commented on Jun 2, 2017 Thanks for reporting!
The runtime implementation of protocol classes will be thoroughly reworked as a part of PEP-544, see also python/typing#417 for a proof of concept runtime implementation.
Also, there is another ongoing discussion python/typing#432 about a global refactoring of typing module that will significantly improve performance.
Therefore, I would wait with any large PRs until these two stories are settled. If you still want to propose a small PR, you can do this at the upstream typing repo https://github.com/python/typing iritkatriel commented on Sep 7, 2022 ilevkivskyi commented on Sep 7, 2022 TBH I am not sure this issue is still relevant (at least I didn't hear any recent complaints about Protocol performance). @orenbenkiki is performance still bad for your application? AlexWaygood commented on Sep 7, 2022 I've seen recent complaints about the performance of Protocol from users of the beartype third-party library, and by @posita here. (I'm not sure I've ever seen a proper write-up of the performance problems in a CPython issue, however.) ilevkivskyi commented on Sep 7, 2022 Hm, actually the short-circuiting proposed in that comment may be a good idea (unless I forgot something) for a simple perf optimization (btw FWIW this is what mypy does internally, it always checks nominal subtypig first). AlexWaygood commented on Sep 7, 2022 @posita appears to have implemented optimised versions of ProtocolMeta here and here.
(I haven't studied the code for either link, but may be worth looking at!) posita commented on Sep 7, 2022
@posita appears to have implemented optimised versions of ProtocolMeta here and here.
(I haven't studied the code for either link, but may be worth looking at!)
For color, the current implementation lives in Beartype and is divided among two classes:
The meat is in _CachingProtocolMeta whereas the Protocol is basically a hack to work around some standard library implementation details and could likely be eliminated. At a high level, _CachingProtocolMeta overrides __instancecheck__ to perform an examination of whether an object "satisfies" a Protocol definition similar to typing._ProtocolMeta.__instancecheck__ and then caches the result by that object's type. Note the asymmetry: the examination is performed on the object, but it is assumed that all objects of the first-examined object's type are consistent. This makes the implementation ill-suited for runtime-composed "types" or monkey-patched objects.
Happy to discuss further, if desired. ilevkivskyi commented on Sep 7, 2022 Caching may need a more careful consideration (especially w.r.t. monkey-patching classes). I was specifically referring to this idea
class _ProtocolMeta(ABCMeta):
# …
def __instancecheck__(cls, instance):
if super().__instancecheck__(instance):
# Short circuit for direct inheritors
return True
else:
# … existing implementation that checks method names, etc. …
return False@posita Do you have any good code base where you can benchmark this w.r.t. current implementation? posita commented on Oct 9, 2022 I can probably do something crude with numerary's and dyce's respective batteries of unit tests. Those are what motivated beartype.typing._typingpep544._CachingProtocolMeta in the first place. Give me a few days and I can probably throw something together. added 4 commits that reference this issue on Dec 4, 2023pythongh-74690: Optimise `isinstance()` and `issubclass()` calls agai… gh-74690: Optimise `isinstance()` and `issubclass()` calls against ru… pythongh-74690: Avoid a costly type check where possible in `_Protoco… gh-74690: Avoid a costly type check where possible in `_ProtocolMeta.… namka279 commented on Jul 21, 2024
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