How Can I Successfully Perform Relative Imports in Python Packages?

Relative Imports in Python

In Python, importing modules from within a package can be a tricky task. Consider the following directory structure:

app/
   __init__.py
   sub1/
      __init__.py
      mod1.py
   sub2/
      __init__.py
      mod2.py

Suppose you're working on mod1.py and need to import something from mod2.py. You might try:

from ..sub2 import mod2

However, this results in an "Attempted relative import in non-package" error. The solution lies in the fact that Python interprets modules run as __main__ (e.g., python mod1.py) as top-level modules, regardless of their file system location.

To enable relative imports, the importing module must not be running as __main__. This can be accomplished by running the interpreter with a package as the main module:

python -m app.sub1.mod1

Alternatively, you can use the __package__ attribute to specify the parent package manually:

import sys
sys.path.insert(0, '..')
from sub2.mod2 import MyClass

This method manipulates the system path, but it does not require running the module as __main__.

However, for relative imports to work within subpackages, it's important to ensure that __init__.py files are present in each directory. These files act as package markers and enable the __package__ attribute to reference the containing package.

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