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isinstance(x, typing.Protocol-class) unexpectedly evaluates properties #89445

Closed as not planned
Closed as not planned
isinstance(x, typing.Protocol-class) unexpectedly evaluates properties#89445
Labels
3.8 (EOL)end of life3.9 (EOL)end of lifetopic-typingtype-bugAn unexpected behavior, bug, or error

Description

@daitakahashi
daitakahashi
mannequin
opened on Sep 24, 2021
BPO 45282
Nosy @AlexWaygood, @daitakahashi
Files
  • test_protocol_property.py: testcases
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    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'

    bugs.python.org fields:

    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

      @daitakahashi
      daitakahashimannequin
      on Sep 24, 2021
      MannequinAuthor

      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 life
      3.9 (EOL)end of life
      type-bugAn unexpected behavior, bug, or error
      on Sep 24, 2021

    3. AlexWaygood commented on Sep 24, 2021

      @AlexWaygood
      AlexWaygood
      on Sep 24, 2021
      Member

      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
      AlexWaygood
      on Mar 5, 2023
      Member

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

    7. AlexWaygood
      closed this as not plannedon Mar 5, 2023
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      3.8 (EOL)end of life3.9 (EOL)end of lifetopic-typingtype-bugAn unexpected behavior, bug, or error

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