[issue47007] [doc] str docs are inconsistent with special method lookup

[miss-islington]

miss-islington  added the comment:


New changeset c0063bdc7b5fed98c6799f3da0a954a775e3d89e by Miss Islington (bot) 
in branch '3.9':
bpo-47007: [doc] `str` special method lookup (GH-31863)
https://github.com/python/cpython/commit/c0063bdc7b5fed98c6799f3da0a954a775e3d89e


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[issue47007] [doc] str docs are inconsistent with special method lookup

[miss-islington]

miss-islington  added the comment:


New changeset f502dadb332f911fa3b6c531bbc5065795cca242 by Miss Islington (bot) 
in branch '3.10':
bpo-47007: [doc] `str` special method lookup (GH-31863)
https://github.com/python/cpython/commit/f502dadb332f911fa3b6c531bbc5065795cca242


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[issue47007] [doc] str docs are inconsistent with special method lookup

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:

Thanks for the report and fix!

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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue47007] [doc] str docs are inconsistent with special method lookup

[miss-islington]

Change by miss-islington :


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pull_request: https://github.com/python/cpython/pull/32319

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[issue47007] [doc] str docs are inconsistent with special method lookup

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:


New changeset bb86d1d9fbd1888524e04475383f4ea764277f67 by Vanshaj Singhania in 
branch 'main':
bpo-47007: [doc] `str` special method lookup (GH-31863)
https://github.com/python/cpython/commit/bb86d1d9fbd1888524e04475383f4ea764277f67


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[issue47007] [doc] str docs are inconsistent with special method lookup

[miss-islington]

Change by miss-islington :


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nosy: +miss-islington
nosy_count: 4.0 -> 5.0
pull_requests: +30379
pull_request: https://github.com/python/cpython/pull/32318

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[issue47007] [doc] str docs are inconsistent with special method lookup

[Vedran Čačić]

Vedran Čačić  added the comment:

You mean `type(object).__str__(object)` instead of `type(object).__str__()`, 
obviously.

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[issue47007] [doc] str docs are inconsistent with special method lookup

[Vanshaj Singhania]

Change by Vanshaj Singhania :


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keywords: +patch
pull_requests: +29961
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/31863

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[issue47007] [doc] str docs are inconsistent with special method lookup

[Raymond Hettinger]

Change by Raymond Hettinger :


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[issue47007] [doc] str docs are inconsistent with special method lookup

[Vanshaj Singhania]

New submission from Vanshaj Singhania :

The documentation for the `str` class[^1] says:

> If neither encoding nor errors is given, str(object) returns object.__str__()

This led our students[^2] to try the following code:

>>> class Test:
... def __str__(self):
... return 'hi'
... 
>>> test = Test()
>>> test.__str__ = lambda self: 'bye'
>>> str(test)

The expected result was calling `test.__str__()`, but instead the interpreter 
output was `'hi'`.

The docs for special method lookup[^3] do say that instance attributes are 
ignored:

> For custom classes, implicit invocations of special methods are only 
> guaranteed to work correctly if defined on an object’s type, not in the 
> object’s instance dictionary.

This makes sense, and explains the observed behavior, but the `str` class docs 
seem to be inconsistent with this. Perhaps it would be more clear if the `str` 
documentation mentioned that it called `type(object).__str__()` instead of 
`object.__str__()`.

[^1]: https://docs.python.org/3/library/stdtypes.html#str
[^2]: CS 61A at UC Berkeley, https://cs61a.org
[^3]: https://docs.python.org/3/reference/datamodel.html#special-method-lookup

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assignee: docs@python
components: Documentation
messages: 415110
nosy: docs@python, itsvs
priority: normal
severity: normal
status: open
title: [doc] str docs are inconsistent with special method lookup
type: enhancement
versions: Python 3.10, Python 3.11, Python 3.9

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