Doc: Namespace Packages: Inconsistent documentation of __loader__ being None

[JulienPalard]

BPO	35181
Nosy	@warsaw, @brettcannon, @ncoghlan, @ericvsmith, @ericsnowcurrently, @JulienPalard, @csabella, @maggyero, @miss-islington
PRs	bpo-35181: Correct an assumption about the namespace package loader attribute #10376 bpo-37800: Clean up importlib documentation for some module attributes #10016 bpo-35181: Correct importlib documentation for some module attributes #15190 [3.9] bpo-35181: Correct importlib documentation for some module attributes (GH-15190) #22872 [3.8] bpo-35181: Correct importlib documentation for some module attributes (GH-15190) #22873

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/warsaw'
closed_at = None
created_at = <Date 2018-11-06.22:29:09.600>
labels = ['type-feature', '3.8', '3.9', '3.10', 'docs']
title = 'Doc: Namespace Packages: Inconsistent documentation of __loader__ being None'
updated_at = <Date 2020-10-24.03:04:47.832>
user = 'https://github.com/JulienPalard'

bugs.python.org fields:

activity = <Date 2020-10-24.03:04:47.832>
actor = 'maggyero'
assignee = 'barry'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2018-11-06.22:29:09.600>
creator = 'mdk'
dependencies = []
files = []
hgrepos = []
issue_num = 35181
keywords = ['patch']
message_count = 12.0
messages = ['329392', '329419', '339814', '341173', '346316', '346317', '379227', '379253', '379254', '379256', '379260', '379512']
nosy_count = 10.0
nosy_names = ['barry', 'brett.cannon', 'ncoghlan', 'eric.smith', 'docs@python', 'eric.snow', 'mdk', 'cheryl.sabella', 'maggyero', 'miss-islington']
pr_nums = ['10376', '10016', '15190', '22872', '22873']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue35181'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[JulienPalard]

The documentation states that a __loader__ of a namespace package should be None:

• 1 "For namespace packages this should be set to None."
• 2 "To indicate to the import machinery that the spec represents a namespace portion. the path entry finder sets “loader” on the spec to None".

But this looks wrong 3, looks like it has been changed in 4/5.

I think one should rely on __file__ being None on namespace packages (which make sense as they span over multiple directories) instead of __loader__ being None (a side effect of the import machinery ?).

[maggyero]

It looks like Barry Warsaw has not been fully updated the documentation after making the __spec__.loader attribute match with the __loader__ attribute, and the __spec__.file attribute match with the __file__ attribute for namespace packages.

Here is a pull request to update the library documentation of importlib (your first link [1]) with the current Barry's implementation:
#10016

Here is another pull request to update the reference documentation of the import system (your second link [2], but for a different paragraph, as I think the "To indicate to the import machinery that the spec represents a namespace portion the path entry finder sets “loader” on the spec to None" sentence is correct, since the _bootstrap.ModuleSpec.loader attribute of a namespace package remains None until the call to the importlib._bootstrap._init_module_attrs function):
#10376

[csabella]

@barry, you started a review of PR10016 and I believe all your requested changes have been made, so please review again when you get a chance. Please also take a look at PR10376. Thanks!

[warsaw]

I've approved both PRs, however I am rather uncomfortable about the code snippet in import.rst. Géry's change is a good one AFAICT, and thanks for the contribution! I would feel much better about the long term correctness of this code snippet if we had a doctest to run over it. But that's for another time.

[maggyero]

@julien, @barry

Now that the PRs are merged, I think that we can close this issue.

[maggyero]

Oops, sorry, only one of the two PRs has been merged.

[warsaw]

Apologies for the long delay in reviewing this bug. I'm looking at it now, however since Python 3.7 is in security-only mode, this will only apply to 3.10, 3.9, and 3.8.