Description

assignee = None
closed_at = None
created_at = <Date 2021-09-24.13:25:14.862>
labels = ['type-bug', '3.8', '3.9']
title = 'isinstance(x, typing.Protocol-class) unexpectedly evaluates properties'
updated_at = <Date 2021-09-24.14:52:18.540>
user = 'https://github.com/daitakahashi'

activity = <Date 2021-09-24.14:52:18.540>
actor = 'AlexWaygood'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-09-24.13:25:14.862>
creator = 'daitakahashi'
dependencies = []
files = ['50303']
hgrepos = []
issue_num = 45282
keywords = []
message_count = 2.0
messages = ['402562', '402567']
nosy_count = 2.0
nosy_names = ['AlexWaygood', 'daitakahashi']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45282'
versions = ['Python 3.8', 'Python 3.9']

Activity

1. daitakahashi commented on Sep 24, 2021

   

   daitakahashimannequin

   on Sep 24, 2021

   MannequinAuthor

   More actions

   Because __instancecheck__ of _ProtocolMeta uses hasattr() and getattr(), both of which evaluate property attributes, calling isinstance() with an object and a class that inherits typing.Protocol evaluates the input object's properties in some cases.

   The attached testcases include three cases of checking subtype relationship of an instance (having a property "x" that may raise RuntimeError on evaluation) and following three protocol classes;
   (1) a protocol class having "x" as a property,
   (2) a protocol class having "x" as a data attribute, and
   (3) a protocol class having "x" as a class property that raises
   RuntimeError on evaluation (>= python 3.9 only).

   Expected behavior:

   1. The isinstance(obj, Protocol_class) does not evaluate anything but just checks existence of attribute names.
   2. All cases in the attached testcases run without any error

   Thank you very much in advance.
2. daitakahashi

   added

   3.8 (EOL)end of lifeend of life

   3.9 (EOL)end of lifeend of life

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Sep 24, 2021
3. AlexWaygood commented on Sep 24, 2021

   

   AlexWaygood

   on Sep 24, 2021

   Member

   More actions

   Related: https://bugs.python.org/issue44904
4. ezio-melotti

   transferred this issue fromon Apr 10, 2022
5. AlexWaygood

   added

   topic-typing

   on Apr 13, 2022
6. AlexWaygood commented on Mar 5, 2023

   

   AlexWaygood

   on Mar 5, 2023

   Member

   More actions

   Duplicate of #102433, which is a newer issue but has more discussion
7. AlexWaygood

   closed this as not plannedon Mar 5, 2023

Issue actions