Issue 35843: importlib.util docs for namespace packages innaccurate

For instance:


# `a` is an empty directory, a PEP 420 namespace package

>>> import importlib.util
>>> importlib.util.find_spec('a')
ModuleSpec(name='a', loader=None, origin='namespace', submodule_search_locations=_NamespacePath(['/tmp/x/a']))


https://docs.python.org/3/library/importlib.html#importlib.machinery.ModuleSpec.origin

> ...  Normally “origin” should be set, but it may be None (the default) which indicates it is unspecified (e.g. for namespace packages).

above the `origin` is `'namespace'`

https://docs.python.org/3/library/importlib.html#importlib.machinery.ModuleSpec.submodule_search_locations

> List of strings for where to find submodules, if a package (None otherwise).

However the `_NamespacePath` object above is not indexable:

>>> x = importlib.util.find_spec('a').submodule_search_locations
>>> x[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '_NamespacePath' object does not support indexing


I can work around however with:

>>> next(iter(x))
'/tmp/x/a'


======================


so I guess a few things can/should come out of this:

- Document the `'namespace'` origin
- Document that `submodule_search_paths` is a Sized[str] instead
- Add `__getitem__` to `_NamespacePath` such that it implements the full `Sized` protocol

Hmmm, it appears this was changed in python3.7 to have `None` for the origin instead of `'namespace'` -- however the `submodule_search_locations` is still not indexable:



>>> importlib.util.find_spec('a')
ModuleSpec(name='a', loader=None, submodule_search_locations=_NamespacePath(['/tmp/x/a']))
>>> importlib.util.find_spec('a').origin
>>> spec = importlib.util.find_spec('a')
>>> spec.submodule_search_locations
_NamespacePath(['/tmp/x/a'])
>>> spec.submodule_search_locations[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '_NamespacePath' object does not support indexing

See also #35673.

Anyone have an opinion about the __getitem__ proposal? I'm fine with it but I wanted to make sure other import + namespace folks don't disagree.

+1

New changeset ab9b31f94737895f0121f26ba3ad718ebbc24fe1 by Miss Islington (bot) (Anthony Sottile) in branch 'master':
bpo-35843: Implement __getitem__ for _NamespacePath (GH-11690)
https://github.com/python/cpython/commit/ab9b31f94737895f0121f26ba3ad718ebbc24fe1

messages: + msg337050

messages: + msg336954