‘Attempted relative import in non-package’ although packages with __init__.py in one directory

Relative imports only work for packages, but when you importing in extended.py you are running a top-level module instead.

The current directory may hold a __init__.py file but that doesn’t make exended.py part of a package yet.

For something to be considered a package, you need to import the directory name instead. The following would work:

main.py

packagename\
    __init__.py
    basic.py
    extended.py

then in main.py put:

import packagename.extended

and only then is extended part of a package and do relative imports work.

The relative import now has something to be relative to, the packagename parent.