None of the below are very serious or likely to mislead anyone using or implementing Python, but...

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3.3.2. Customizing attribute access

The docs for `__dir__` say:

> A sequence must be returned. dir() converts the returned sequence to a list and sorts it.

At least in CPython and PyPy, this isn't enforced; any iterable can be returned (and it's then converted to a list and sorted). You can even make `__dir__` a generator function. (I've never seen that in the wild--but I have seen code that returns a `map` iterator.)

I think it would be better to say "An iterable must be returned. dir() converts the returned iterable to a list and sorts it."

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3.3.2.3. __slots__

> This class variable can be assigned a string, iterable, or sequence of strings...

While it's true that you can assign any iterable, it's at best misleading to assign an iterator. For example, if you use `__slots__ = iter('abc')`, you will get a class with descriptors named `a`, `b`, and `c`, but with an empty iterator in `__slots__`. There's probably no reason to actually outlaw that, but it might be worth noting in 3.3.2.3.1 along with the other weird possibilities like assigning a mapping.

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3.3.6. Emulating container types

The docs still say that the ABCs are in `collections` rather than `collections.abc`.

> ... for mappings, __iter__() should be the same as keys()

No; `__iter__()` should be an iterator over the keys; `keys()` _can_ be an iterator, but generally should be a view instead.

> The membership test operators (in and not in) are normally implemented as an iteration through a sequence. However, container objects can supply the following special method with a more efficient implementation, which also does not require the object be a sequence.

I don't think this should say "through a sequence". They're implemented as iteration through whatever the container is, whether it's a sequence, a set, a linked list, or anything else. The documentation on `__contains__` immediately below clarifies this, but it's probably better to be clear from the start.

Hi, I've taken a look at these suggestions and the documentation and I've posted a patch to get things moving :)

A couple of points about the suggested changes that I haven't included in the patch:

1) I think changing the documentation for __dir__() to say it can return an iterable needs some discussion.

The documentation also says:
"The ``__dir__`` function should accept no arguments, and return a list of strings that represents the names accessible on module. If present, this function overrides the standard :func:`dir` search on a module."
And this should definitely be updated from "list of strings" to either "sequence of strings" or "iterable of strings".

However, I'm not sure about updating docs to include "accidental" functionality - looking at the testing, news, and documentation from commit https://github.com/python/cpython/commit/3bbb72265411585e64a5d2ccb5ba51763f20e311 the intention was to allow __dir__ to return a sequence.

I think updating the docs to say __dir__ should return an iterator would be a separate issue which would also include test enchancements, so I've left that change out of my patch and I've just corrected the line I've quoted above.

2) > The docs still say that the ABCs are in `collections` rather than `collections.abc`.

I couldn't find an instance of this, it's probably been corrected at some point.

Any thoughts on the above, the other suggestions, or the patch?

Can you please turn this into a regular PR?

dorosch, please note section 3.9 from the developers guide:

"When a patch exists in the issue tracker that should be converted into a GitHub pull request, please first ask the original patch author to prepare their own pull request. If the author does not respond after a week, it is acceptable for another contributor to prepare the pull request based on the existing patch."

It's been two hours, not a week, and I would've liked to raise a pull request for this change.

I've decided to raise a pull request for the patch, considering it's only been a few hours.

New changeset 4544e78ec4558b75bf95e5b7dfc1b5bbb07ae5f0 by Raymond Hettinger (alclarks) in branch 'master':
bpo-25866: Minor cleanups to "sequence" in docs (GH-17177)
https://github.com/python/cpython/commit/4544e78ec4558b75bf95e5b7dfc1b5bbb07ae5f0

New changeset 72321c7be096434e3343bd5b37a4436aa9eea098 by Raymond Hettinger (Miss Islington (bot)) in branch '3.7':
bpo-25866: Minor cleanups to "sequence" in docs (GH-17177) (GH-17209)
https://github.com/python/cpython/commit/72321c7be096434e3343bd5b37a4436aa9eea098

New changeset 20a4f6cde65549fd0252eb8c879963e0e8b40390 by Raymond Hettinger (Miss Islington (bot)) in branch '3.8':
bpo-25866: Minor cleanups to "sequence" in docs (GH-17177) (GH-17208)
https://github.com/python/cpython/commit/20a4f6cde65549fd0252eb8c879963e0e8b40390