How to fix "A relative import attempt was made from a non-package even though there is __init__.py" error

Question

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

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

In core_test.py I have the following import statement

from ..components.core import GameLoopEvents

However, when I run, I get the following error:

tests$ python core_test.py
Traceback (most recent call last):
  File "core_test.py", line 3, in <module>
    from ..components.core import GameLoopEvents
ValueError: Attempted relative import in non-package

I found "relative path not working even with __init__.py" and "Import a module from a relative path" in my search, but they didn't help.

Is there anything I'm missing here?

Answer 1

To elaborate on Ignacio Vazquez-Abrams’s answer:

Python’s import mechanism is __name__ relative to the current file. When a file is executed directly, its name is not the usual name, but "__main__" is used as the name. Therefore, relative imports don't work.

As Ignacio suggested, you can execute it using the -m option. If part of your package is run as a script, you can also use the __package__ attribute to tell the file what name it should have in the package hierarchy.

For more information, please see http://www.python.org/dev/peps/pep-0366/.

Answer 2

Yes. You are not using it as a package.

python -m pkg.tests.core_test