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bpo-35105: Document that CPython accepts "invalid" identifiers #11263

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Windsooon
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@Windsooon Windsooon commented Dec 20, 2018

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@terryjreedy terryjreedy left a comment

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That you for proposing something specific to chew on. I think spelling, grammar, and content all need tweaking.

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A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

@zhangyangyu
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Do we really need to mention this?

@terryjreedy
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That discussion is on the issue.

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I don't think we can mark this as an implementation detail for setattr(). The details are downstream and determined by the target object, not by setattr itself.

Suggested wording:

Note, setattr() attempts to update the object with the given attr/value pair.
Whether this succeeds and what its affect is is determined by the target object.
If an object's class defines `__slots__`, the attribute may not be writeable.
If an object's class defines property with a setter method, the *setattr()*
will trigger the setter method which may or may not actually write the attribute.
For objects that have a regular dictionary (which is the typical case), the
*setattr()* call can make any string keyed update allowed by the dictionary
including keys that aren't valid identifiers -- for example setattr(a, '1', 'one')
will be the equivalent of vars()['1'] ='one'.

This issue has little to do with setattr() and is more related to the fact that instance dictionaries can hold any valid key. In a way, it is no different than a user writing a.__dict__['1'] = 'one'. That has always been allowed and the __dict__ attribute is documented as writeable, so a user is also allowed to write `a.dict = {'1': 'one'}.

In short, we can talk about this in the setattr() docs but it isn't really a setattr() issue. Also, the behavior is effectively guaranteed by the other things users are allowed to do, so there is no merit in marking this as an implementation detail. Non-identifier keys can make it into an instance dictionary via multiple paths that are guaranteed to work.

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I agree with Raymond's revision. Note that it would replace the entire proposed addition, including the impl-detail directive. By adding more 'meat', it makes an addition more worthwhile.

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The whole note needs to be indented for proper alignment.

@JulienPalard
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Hi @Windsooon thanks for this PR! Would you have some time to integrate Cheryl comments?

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I just updated it. Thank you @csabella

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LGTM with nits (all can be accepted right from github).

@@ -1388,6 +1388,17 @@ are always available. They are listed here in alphabetical order.
object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to
``x.foobar = 123``.

.. note::

setattr() attempts to update the object with the given attr/value pair.
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@JulienPalard JulienPalard Sep 12, 2019

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Suggested change
setattr() attempts to update the object with the given attr/value pair.
``setattr()`` attempts to update the object with the given attr/value pair.


setattr() attempts to update the object with the given attr/value pair.
Whether this succeeds and the effect it has determined by the target object.
If an object's class defines `__slots__`, the attribute may not be writeable.
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Suggested change
If an object's class defines `__slots__`, the attribute may not be writeable.
If an object's class defines ``__slots__``, the attribute may not be writeable.

For objects that have a regular dictionary (which is the typical case), the
*setattr()* call can make any string keyed update allowed by the dictionary
including keys that aren't valid identifiers -- for example ``setattr(a, '1', 'one')``
will be the equivalent of ``vars()['1'] ='one'``.
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Suggested change
will be the equivalent of ``vars()['1'] ='one'``.
will be the equivalent of ``vars()['1'] = 'one'``.

@csabella
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@Windsooon, please address the review comments from Julien. Thanks!

@AlexWaygood
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Changes were requested on this PR by a core dev over two years ago, but have not been applied. There is also now a merge conflict. I am therefore closing this PR.

@Windsooon, if you're still interested in working on this, feel free to open a new PR. Alternatively, ping me, and I'll happily reopen the PR. Thanks! 🙂

@Windsooon
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@AlexWaygood I'm so sorry for missing the notification from CPython, I will catch up in a few weeks.

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@Windsooon no worries!

@@ -1388,6 +1388,17 @@ are always available. They are listed here in alphabetical order.
object allows it. For example, ``setattr(x, 'foobar', 123)`` is equivalent to
``x.foobar = 123``.

.. note::

setattr() attempts to update the object with the given attr/value pair.
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(in addition to the above)

Suggested change
setattr() attempts to update the object with the given attr/value pair.
setattr() attempts to update the object with the given attribute/value pair.

or

Suggested change
setattr() attempts to update the object with the given attr/value pair.
setattr() attempts to update the object with the given attribute-value pair.

.. note::

setattr() attempts to update the object with the given attr/value pair.
Whether this succeeds and the effect it has determined by the target object.
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Suggested change
Whether this succeeds and the effect it has determined by the target object.
Whether this succeeds and the effect it has is determined by the target object.

setattr() attempts to update the object with the given attr/value pair.
Whether this succeeds and the effect it has determined by the target object.
If an object's class defines `__slots__`, the attribute may not be writeable.
If an object's class defines :class:`property` with a setter method, the *setattr()*
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*setattr()* -> `setattr()` here and below (I think * is commonly used for parameters)

will trigger the setter method which may or may not actually write the attribute.
For objects that have a regular dictionary (which is the typical case), the
*setattr()* call can make any string keyed update allowed by the dictionary
including keys that aren't valid identifiers -- for example ``setattr(a, '1', 'one')``
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Would you happen to have an example of this behavior? I'm not quite following what it's doing (how a turns into vars())

If an object's class defines :class:`property` with a setter method, the *setattr()*
will trigger the setter method which may or may not actually write the attribute.
For objects that have a regular dictionary (which is the typical case), the
*setattr()* call can make any string keyed update allowed by the dictionary
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Suggested change
*setattr()* call can make any string keyed update allowed by the dictionary
*setattr()* call can make any string-keyed update allowed by the dictionary

@AlexWaygood
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I think this PR has now been superseded by #96454

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