Raise ImportWarning when loader.load_module() is used

[brettcannon]

BPO	26131
Nosy	@brettcannon, @ncoghlan, @vstinner, @ericsnowcurrently, @webknjaz, @MichaelAnckaert, @brandtbucher, @nanjekyejoannah
PRs	bpo-26131: deprecate the use of load_module() #22905 gh-70319: Deprecate usage of load_module() #23469

^{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 2020-12-07.21:27:33.787>
created_at = <Date 2016-01-15.21:44:04.899>
labels = ['interpreter-core', 'type-bug']
title = 'Raise ImportWarning when loader.load_module() is used'
updated_at = <Date 2020-12-14.13:06:12.676>
user = 'https://github.com/brettcannon'

bugs.python.org fields:

activity = <Date 2020-12-14.13:06:12.676>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-12-07.21:27:33.787>
closer = 'brett.cannon'
components = ['Interpreter Core']
creation = <Date 2016-01-15.21:44:04.899>
creator = 'brett.cannon'
dependencies = []
files = []
hgrepos = []
issue_num = 26131
keywords = ['patch']
message_count = 14.0
messages = ['258333', '347561', '347580', '349284', '349286', '349287', '349295', '379389', '382548', '382796', '382799', '382801', '382874', '382986']
nosy_count = 8.0
nosy_names = ['brett.cannon', 'ncoghlan', 'vstinner', 'eric.snow', 'webknjaz', 'michaelanckaert', 'brandtbucher', 'nanjekyejoannah']
pr_nums = ['22905', '23469']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26131'
versions = ['Python 3.6']

[brettcannon]

Since loader.load_module() is documented as deprecated, we should consider raising an ImportWarning when it is used. That way when Python 2.7 support ends we can either remove it or have one more release where the various ImportWarnings turn into DeprecationWarnings and we finally clean up the import semantics to only be spec-based.

[nanjekyejoannah]

@brett Since this was opened like years ago. Before I work on it, I was wondering If it is still relevant.

[brettcannon]

@joannah no clue if this ever happened. Could you check the code if DeprecationWarning is being raised yet?

[MichaelAnckaert]

I checked out the source (Lib/imp.py:219) and only see the docstring marking this method als Deprecated. No exceptions are being raised.

I would like to work on this issue.

[MichaelAnckaert]

Clarification: the imp module shows a DeprecationWarning when imported. Was this what was meant?

[nanjekyejoannah]

Feel free to open a PR.

[brettcannon]

If you look at https://github.com/python/cpython/blob/master/Lib/importlib/_bootstrap.py and https://github.com/python/cpython/blob/master/Lib/importlib/_bootstrap_external.py you will notice a bunch of comments near all the calls to load_module(). Those are the places that should be somehow triggering a DeprecationWarning.

I think there's a compatibility shim function which would need to raise an exception so that anyone who has implemented load_module() as the only way to handle loading get a warning (but I think that requires certain loaders to have appropriate support which hopefully they have already but someone needs to double-check). After that every implementation of load_module() should have a warning.

[brettcannon]

A PR is now up. I ended up deprecating the load_module() methods in importlib itself and then raise ImportWarning in the import system itself when falling back to load_module().

[brettcannon]

New changeset 2de5097 by Brett Cannon in branch 'master':
bpo-26131: Deprecate usage of load_module() (GH-23469)
2de5097

[brandtbucher]

I'm seeing the following test failure locally on master (doesn't seem to be showing up in CI though). I'm not too familiar with this stuff, but it looks related to this change:

======================================================================
FAIL: test_all (test.test___all__.AllTest) (module='distutils.command')
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/bucher/src/cpython/Lib/test/test___all__.py", line 55, in check_all
    self.assertEqual(keys, all_set, "in module {}".format(modname))
  File "/home/bucher/src/cpython/Lib/contextlib.py", line 140, in __exit__
    next(self.gen)
  File "/home/bucher/src/cpython/Lib/test/support/warnings_helper.py", line 177, in _filterwarnings
    raise AssertionError("unhandled warning %s" % reraise[0])
AssertionError: unhandled warning {message : ImportWarning('VendorImporter.exec_module() not found; falling back to load_module()'), category : 'ImportWarning', filename : '<frozen importlib._bootstrap>', lineno : 681, line : None}

---

Should we be ignoring the new warning in this test as well? I'm still not sure why I seem to be the only one seeing it.

[brettcannon]

What is "VendorImporter" (see the message of the ImportWarning)? That's not in the stdlib, so it looks like your system is injecting something via some .pth file or environment variable that doesn't define exec_module().

[brandtbucher]

Yep, looks like that was it. Thanks!