bpo-30969: Fix docs about the comparison in absence of __contains__ #2761
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Both the `__iter__` and the index-iteration method test the `is` first. While the document says that `x is x` means that `x == x` should be true, it is not true for example in the case of `nan`.
```>>> x = float('nan')
>>> x == x
False
>>> x is x
True
>>> class Foo:
... def __iter__(self):
... return iter([x])
...
>>> x in Foo()
True
>>> any(x == i for i in Foo())
False
>>> class Bar:
... def __getitem__(self):
... return [x].__getitem__(self)
...
>>> class Bar:
... def __getitem__(self, i):
... return [x].__getitem__(i)
...
>>> x in Bar
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: argument of type 'type' is not iterable
>>> x in Bar()
True
>>> any(x == i for i in Bar())
False```
|
@ztane, thanks for your PR! By analyzing the history of the files in this pull request, we identified @birkenfeld, @vadmium and @benjaminp to be potential reviewers. |
rhettinger
approved these changes
Dec 24, 2018
tirkarthi
reviewed
Jan 8, 2019
Doc/reference/expressions.rst
Outdated
| :meth:`__iter__`, ``x in y`` is ``True`` if some value ``z`` with ``x == z`` is | ||
| produced while iterating over ``y``. If an exception is raised during the | ||
| iteration, it is as if :keyword:`in` raised that exception. | ||
| :meth:`__iter__`, ``x in y`` is ``True`` if some value ``z``, for which the |
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@ztane trailing space in the three lines are causing CI failure. Removing them will fix the issue. Thanks for the patch.
Doc git:(pr_2761) python3 tools/rstlint.py -i tools -i ./venv -i README.rst
[1] reference/expressions.rst:1446: trailing whitespace
[1] reference/expressions.rst:1447: trailing whitespace
[1] reference/expressions.rst:1448: trailing whitespace
3 problems with severity 1 found.
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@ztane, please apply the suggestions from @tirkarthi to fix the CI failures. Thanks! |
csabella
approved these changes
May 30, 2019
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…ythonGH-2761) (cherry picked from commit 2f5b9dc) Co-authored-by: Antti Haapala <[email protected]>
|
GH-13684 is a backport of this pull request to the 3.7 branch. |
miss-islington
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…H-2761) (cherry picked from commit 2f5b9dc) Co-authored-by: Antti Haapala <[email protected]>
DinoV
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The documentation doesn't match the implementation, which clearly does
x is y or x == yto check ifxis the elementyfrom a container. Both the__iter__and the index-iteration method test the elements usingisfirst. While the document says thatx is xmeans thatx == xshould be true, it is not true for example in the case ofnan: