Python

Are `__init__.py` Files Required in Every Subfolder?

Short Answer:

No, but it depends on:

  • Python version being used
  • Package structure requirements
  • Specific functionality needed

Detailed Breakdown:

1. Python Version Considerations

  • Python < 3.3: Required in every directory to be recognized as a package
  • Python 3.3+: Not strictly required (namespace packages) but still commonly used

2. When They're Not Required:

  • Namespace Packages (Python 3.3+)
  • Directories containing only data/configuration files
  • Subfolders not meant to be imported directly
  • When using implicit namespace packages

3. When They're Required:

  • Traditional (Regular) Packages (even in Python 3.3+)
  • When using relative imports between modules
  • To define __all__ for public API
  • When initializing package-level state

Example Scenarios:

1. Traditional Package Structure (requires __init__.py)

my_package/
    __init__.py
    utils/
        __init__.py
        helpers.py
    models/
        __init__.py
        base.py

2. Namespace Package Structure (no __init__.py)

my_package/
    core/
        calculations.py  # No __init__.py needed
    web/
        routing.py      # No __init__.py needed

Key Exceptions:

  • Required if you need to:
    • Import from sibling modules (from ..utils import helpers)
    • Maintain backward compatibility with older Python versions
    • Use package initialization hooks
    • Control module exposure with __all__

Best Practice Recommendations:

  1. Include __init__.py in subfolders if:

    • You need to import between submodules
    • You want explicit package declaration
    • Working with legacy codebases

  2. Omit __init__.py if:

    • Creating namespace packages (Python 3.3+)
    • Directories are just organizational containers
    • You want to avoid package initialization overhead

  3. Hybrid Approach:

# my_package/__init__.py
__path__ = __import__('pkgutil').extend_path(__path__, __name__)