What Does Python's __init__.py Do? - Real Python

"A directory without an __init__.py file becomes a namespace package, which behaves differently from a regular package and may cause slower imports. You can use __init__.py to explicitly define a package's public API by importing specific modules or functions into the package namespace."

"The Python convention of using leading underscores helps indicate to users which objects are intended as non-public, although this convention can still be bypassed. Code inside __init__.py runs only once during the first import, even if you run the import statement multiple times."

"Understanding how to effectively use __init__.py helps you structure your Python packages in a clear, maintainable way, improving usability and namespace management."

The __init__.py file is essential for creating regular Python packages, distinguishing them from namespace packages which import more slowly. This file executes automatically during the first import of its containing package and runs only once regardless of repeated import statements. Developers can use __init__.py to initialize package-level variables, define functions or classes, and explicitly structure the package's public API by importing specific modules or functions into the package namespace. Python conventions using leading underscores indicate non-public objects, though these can be bypassed. Effective use of __init__.py improves package structure, maintainability, usability, and namespace management.

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