Package Discovery and __init__.py

When you work with packages in Python, the presence or absence of an __init__.py file in a directory determines how Python treats that directory during import. Historically, any directory intended to be a package must contain an __init__.py file. This file marks the directory as a Python package and enables the interpreter to import modules from it.

Python 3.3 and later introduced implicit namespace packages, which allow you to create packages without an __init__.py file. If you omit __init__.py, Python still recognizes the directory as a package, but only for the purpose of grouping subpackages and modules across multiple locations on the filesystem. This is useful for large projects or plugin systems. However, explicit packages—those with an __init__.py—are still the most common and compatible approach, ensuring clear package boundaries and predictable import behavior.

Choosing between implicit and explicit packages impacts how Python discovers and loads your code:

• Explicit packages are generally preferred for most projects;
• They work reliably with standard tools;
• They make your package structure clear to both Python and other developers.