How to fix “Attempted relative import in non-package” even with __init__.py

Question

I\'m trying to follow PEP 328, with the following directory structure:

pkg/
  __init__.py
  components/
    core.py
    __init__.py
  tests/
    core_test.py         


        

Answer 1

Issue is with your testing method,

you tried python core_test.py

then you will get this error ValueError: Attempted relative import in non-package

Reason: you are testing your packaging from non-package source.

so test your module from package source.

if this is your project structure,

pkg/
  __init__.py
  components/
    core.py
    __init__.py
  tests/
    core_test.py
    __init__.py

cd pkg

python -m tests.core_test # dont use .py

or from outside pkg/

python -m pkg.tests.core_test

single . if you want to import from folder in same directory . for each step back add one more.

hi/
  hello.py
how.py

in how.py

from .hi import hello

incase if you want to import how from hello.py

from .. import how

Answer 2

My quick-fix is to add the directory to the path:

import sys
sys.path.insert(0, '../components/')

Answer 3

Try this

import components
from components import *

Answer 4

As Paolo said, we have 2 invocation methods:

1) python -m tests.core_test
2) python tests/core_test.py

One difference between them is sys.path[0] string. Since the interpret will search sys.path when doing import, we can do with tests/core_test.py:

if __name__ == '__main__':
    import sys
    from pathlib import Path
    sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
    from components import core
    <other stuff>

And more after this, we can run core_test.py with other methods:

cd tests
python core_test.py
python -m core_test
...

Note, py36 tested only.

Answer 5

Yes. You're not using it as a package.

python -m pkg.tests.core_test

Answer 6

To elaborate on Ignacio Vazquez-Abrams's answer:

The Python import mechanism works relative to the __name__ of the current file. When you execute a file directly, it doesn't have its usual name, but has "__main__" as its name instead. So relative imports don't work.

You can, as Igancio suggested, execute it using the -m option. If you have a part of your package that is meant to be run as a script, you can also use the __package__ attribute to tell that file what name it's supposed to have in the package hierarchy.

See http://www.python.org/dev/peps/pep-0366/ for details.