pkgutil.get_loader() fails on "__main__"

[ericsnowcurrently]

BPO	21200
Nosy	@brettcannon, @ncoghlan, @larryhastings, @ericsnowcurrently
Files	issue21200-pkgutil-main.diff

^{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 = <Date 2014-04-19.06:20:35.397>
created_at = <Date 2014-04-11.14:07:35.554>
labels = ['type-bug', 'library', 'release-blocker']
title = 'pkgutil.get_loader() fails on "__main__"'
updated_at = <Date 2014-04-19.06:20:35.395>
user = 'https://github.com/ericsnowcurrently'

bugs.python.org fields:

activity = <Date 2014-04-19.06:20:35.395>
actor = 'eric.snow'
assignee = 'none'
closed = True
closed_date = <Date 2014-04-19.06:20:35.397>
closer = 'eric.snow'
components = ['Library (Lib)']
creation = <Date 2014-04-11.14:07:35.554>
creator = 'eric.snow'
dependencies = []
files = ['34808']
hgrepos = []
issue_num = 21200
keywords = ['patch', '3.4regression']
message_count = 5.0
messages = ['215926', '216043', '216048', '216847', '216848']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'ncoghlan', 'larry', 'python-dev', 'eric.snow']
pr_nums = []
priority = 'release blocker'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21200'
versions = ['Python 3.4', 'Python 3.5']

[ericsnowcurrently]

Prior to 3.4, pkgutil.get_loader('__main__') would return None. Now it results in an ImportError. That's because it calls importlib.util.find_spec() which fails if an existing module does not have __spec__ or it is None.

[ericsnowcurrently]

Here's a patch that checks for modules that don't have __spec__ set.

The patch will fix the problem. However note that the docs and docstring imply (to me) that we should turn any ImportError coming out of the find_loader() call into returning None. Fixing that will also fix this bug, so this patch may be unnecessary.

[ericsnowcurrently]

I've opened bpo-21211 to more directly address the find_loader() issue.

[python-dev]

New changeset bc4eb1b3db5d by Eric Snow in branch '3.4':
Issue bpo-21200: Return None from pkgutil.get_loader() when __spec__ is missing.
http://hg.python.org/cpython/rev/bc4eb1b3db5d

[ericsnowcurrently]

The change is pretty minor so I went ahead and pushed it. To be honest, we should consider deprecating both get_loader and find_loader. I'm just not going to worry about it right now. :)