Description

assignee = None
closed_at = <Date 2021-08-05.00:08:48.071>
created_at = <Date 2020-09-03.20:30:50.412>
labels = ['3.7', '3.8', '3.9', '3.10', 'type-feature', 'docs']
title = 'docs: operator dunder (`__add__`, et al.) invocations described incorrectly'
updated_at = <Date 2021-08-05.00:08:48.071>
user = 'https://github.com/wchargin'

activity = <Date 2021-08-05.00:08:48.071>
actor = 'brett.cannon'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-08-05.00:08:48.071>
closer = 'brett.cannon'
components = ['Documentation']
creation = <Date 2020-09-03.20:30:50.412>
creator = 'wchargin'
dependencies = []
files = []
hgrepos = []
issue_num = 41706
keywords = ['patch']
message_count = 2.0
messages = ['376316', '398954']
nosy_count = 3.0
nosy_names = ['brett.cannon', 'docs@python', 'wchargin']
pr_nums = ['22084']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41706'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']

Activity

1. wchargin commented on Sep 3, 2020

   

   wcharginmannequin

   on Sep 3, 2020

   MannequinAuthor

   More actions

   The operator override dunder methods, like __add__, are described in
   the “Data model” docs here:
   https://docs.python.org/3.10/reference/datamodel.html#object.__add__

   Those docs say:

   For instance, to evaluate the expression x + y, where x is an
   instance of a class that has an __add__() method, x.__add__(y) is
   called.

   But this is not correct: x + y always uses type(x).__add__, which
   may be different from x.__add__ if __add__ has been set directly on
   the instance.

   Demonstration:

   class C:
       def __add__(self, other):
           return "from class"
   
   
   c = C()
   print(c + c)  # prints "from class"
   
   c.__add__ = lambda other: "from instance"
   print(c.__add__(c))  # prints "from instance"
   print(type(c).__add__(c, c))  # prints "from class"
   
   print(c + c)  # prints "from class"!
   

   The same issue appears in the reversed operator dunder (__radd__,
   et al.) docs below.

   I have a patch that I can submit as a PR; just need a bpo number.
2. wchargin

   added

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   on Sep 3, 2020
3. wchargin

   assigned

   docspython

   on Sep 3, 2020
4. wchargin

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   type-featureA feature request or enhancementA feature request or enhancement

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   3.9 (EOL)end of lifeend of life

   3.10 (EOL)end of lifeend of life

   on Sep 3, 2020
5. wchargin

   assigned

   docspython

   on Sep 3, 2020
6. wchargin

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   type-featureA feature request or enhancementA feature request or enhancement

   on Sep 3, 2020
7. brettcannon commented on Aug 4, 2021

   

   brettcannon

   on Aug 4, 2021

   Member

   More actions

   New changeset 80f33f2 by William Chargin in branch 'main':
   bpo-41706: Fix special method invocation docs to mention using type() (GH-22084)
   80f33f2
8. brettcannon

   closed this as completedon Aug 5, 2021
9. brettcannon

   closed this as completedon Aug 5, 2021
10. ezio-melotti

    transferred this issue fromon Apr 10, 2022

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