ImportWarning: can't resolve package from __spec__ or __package__

[blueyed]

Given the following directory structuce:

.
└── tests
    ├── conftest.py
    ├── __init__.py
    ├── relative.py
    └── test_foo.py

With tests/conftest.py:

from .relative import relative

print("conftest")

tests/relative.py:

relative = 1

tests/test_foo.py:

def test_foo():
    pass

Running PYTHONWARNINGS=all pytest tests -s shows:

…/pyenv/tmp-system-ImportWarning-ZniFiE/lib/python3.6/site.py:165: DeprecationWarning: 'U' mode is deprecated
  f = open(fullname, "rU")
…/Vcs/pytest/_pytest/assertion/rewrite.py:7: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  import imp
…/Vcs/pytest/ImportWarning/tests/conftest.py:1: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
  from .relative import relative
conftest
==================================== test session starts ====================================
platform linux -- Python 3.6.3, pytest-3.3.2.dev14+gd3b54d03.d20171225, py-1.5.2, pluggy-0.6.0
rootdir: …/Vcs/pytest, inifile: tox.ini
collected 1 item                                                                            

tests/test_foo.py .                                                                   [100%]

================================= 1 passed in 0.01 seconds ==================================

The ImportWarning is:

tests/conftest.py:1: ImportWarning: can't resolve package from spec or package, falling back on name and path
from .relative import relative

It only shows up when using -s.

This came up for pytest-django.
See pytest-dev/pytest-django#546 (comment).

Defining __package__ explicitly fixes it, but it looks like this should not be necessary.

[pytestbot]

GitMate.io thinks the contributor most likely able to help you is @nicoddemus.

[asottile]

Now that pytest-xdist uses explicit relative imports (after pytest-dev/pytest-xdist#242) this is also breaking the py36-xdist suite for pytest's tests.

[nicoddemus]

Opened #3096 to at least ignore the warning for now so we can get clean builds again.

Anybody knows what's the proper fix here? Who's doing something wrong, pytest or pytest-xdist?

[asottile]

without any evidence my guess would be pytest (and if I were to extend that guess further, it would go away with assert rewriting off).

Let's validate those guesses:

$ PYTHONWARNINGS=all py.test tests -s --assert=plain >& assert_plain.txt
$ PYTHONWARNINGS=all py.test tests -s >& assert_rewrite.txt
$ diff -u assert_*.txt
--- assert_plain.txt	2018-01-08 14:42:20.156677858 -0800
+++ assert_rewrite.txt	2018-01-08 14:42:28.528677858 -0800
@@ -24,3 +24,5 @@
   params = attr.ib(convert=attr.converters.optional(tuple))
 /tmp/foo/venv/lib/python3.6/site-packages/_pytest/fixtures.py:846: DeprecationWarning: The `convert` argument is deprecated in favor of `converter`.  It will be removed after 2019/01.
   ids = attr.ib(default=None, convert=_ensure_immutable_ids)
+/tmp/foo/tests/conftest.py:1: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
+  from .relative import relative

🤔 hmmm... indeed.

Then it would probably be the way pytest is building module objects for __init__ files (with incorrect __package__)?

[asottile]

probably worth reading as well: https://www.python.org/dev/peps/pep-0451/

[BoboTiG]

I have similar warnings, let me know if it needs a separate issue or a pytest-cov issue.

platform win32 -- Python 3.6.5, pytest-3.6.1, py-1.5.3, pluggy-0.6.0 -- C:\python-3.6.5\python.exe
plugins: cov-2.5.1

C:\python-3.6.5\lib\site-packages\pytest_cov\plugin.py:8: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
  from . import embed

C:\python-3.6.5\lib\site-packages\pytest_cov\plugin.py:9: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
  from . import engine

C:\python-3.6.5\lib\site-packages\pytest_cov\engine.py:11: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
  from .compat import StringIO

C:\python-3.6.5\lib\site-packages\pytest_cov\plugin.py:10: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
  from . import compat

[RonnyPfannschmidt]

its the same problem -

[blueyed]

Ping @flub - any idea?