PyCapsule_Import fails when name is in the form 'package.module.capsule'

[lekma]

BPO	32414
Nosy	@ncoghlan, @encukou, @lekma, @skrah, @ericsnowcurrently, @serhiy-storchaka
PRs	bpo-32414: use string after the last dot as the capsule name in PyCapsule_Import #4988 gh-76595: PyCapsule_Import() now imports submodules if needed. #6898

^{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 = None
closed_at = None
created_at = <Date 2017-12-23.09:47:09.382>
labels = ['interpreter-core', 'type-bug', '3.8']
title = "PyCapsule_Import fails when name is in the form 'package.module.capsule'"
updated_at = <Date 2018-05-17.13:34:57.066>
user = 'https://github.com/lekma'

bugs.python.org fields:

activity = <Date 2018-05-17.13:34:57.066>
actor = 'ncoghlan'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2017-12-23.09:47:09.382>
creator = 'lekma'
dependencies = []
files = []
hgrepos = []
issue_num = 32414
keywords = ['patch']
message_count = 15.0
messages = ['308950', '308990', '308994', '315944', '316079', '316123', '316735', '316794', '316795', '316798', '316799', '316805', '316915', '316923', '316927']
nosy_count = 6.0
nosy_names = ['ncoghlan', 'petr.viktorin', 'lekma', 'skrah', 'eric.snow', 'serhiy.storchaka']
pr_nums = ['4988', '6898']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32414'
versions = ['Python 3.8']

Linked PRs

• gh-76595: Add note on PyCapsule_Import behavior #134022

[lekma]

When capsule name is in the form 'package.module.capsule', PyCapsule_Import fails with an AttributeError (module is never an attribute of package).

[serhiy-storchaka]

PR 4988 will break the case 'module.attr.capsule' if 'module.attr' is not a module.

[lekma]

PR 4988 will break the case 'module.attr.capsule' if 'module.attr' is
not a module.
you are right, but is that a case you would expect in an import
statement?

[lekma]

thinking out loud here: maybe both behavior can be exposed, i.e. a PyCapsule_Import that would expect a valid import statement and a Py_GetCapsule that would behave more like getattr?

[encukou]

An option would be to use a colon to separate the module(s) from the attribute(s). The "inspect" module CLI does this, for example:
https://docs.python.org/3/library/inspect.html#command-line-interface

$ python3 -m inspect urllib.parse:SplitResult.geturl
    def geturl(self):
        return urlunsplit(self)

A colon can't appear in an identifier, so the old way can be used if there's no colon in the argument, making this backwards compatible.

[ncoghlan]

"package.module:attribute" is also the syntax used in packaging tools to unambiguously separate the name of the module to be imported from the attribute chain to be looked up within that module: https://packaging.python.org/specifications/entry-points/

So +1 from me for extending it to this use case as well.

[ericsnowcurrently]

+1 on using ":" as the separator.

[serhiy-storchaka]

Using ":" makes the syntax irregular. "package.module:attribute", but "module.attribute". And "package.module.attribute" works too if "package.module" already is imported.

It is possible to support importing submodules without using ":".

[skrah]

I'm sorry if this interrupts the discussion, but isn't this

https://github.com/plures/xnd/blob/06f6dd82dda9c7bca5df30b121b5cd75c6337609/python/xnd/pyxnd.h#L103

of the form package.module.capsule?

This works, and I just want to make sure it continues to do so.

[skrah]

Ah, Serhiy stated the reason (module already imported) previously. Sorry for the noise.

[serhiy-storchaka]

In your case importing xnd automatically imports xnd._xnd and sets it as an attribute of xnd. This case works now. PR 6898 adds support for cases when a submodule is not imported automatically by importing a package.

[encukou]

Is "package.module:namespace.attribute" worth supporting? I guess it isn't, at least for now. So Serhyi's patch will work.