What is the Purpose of `__init__.py` in Python Packages?

The Role of __init__.py in Python Source Directories

Package directory structures in Python often include an __init__.py file. This file plays a crucial role in initializing packages and defining their behavior.

The purpose of __init__.py is to make a directory a Python package. Packages are modules (in the .py file format) that contain other modules (subpackages) and or packages (nested directories with __init__.py). When Python imports a package, it checks for the __init__.py file in the directory and executes it as a module.

Therefore, the __init__.py file can:

• Define module-level attributes that are then available to the entire package.
• Import and initialize other Python modules that are part of the package.
• Control the package's behavior by setting up event handlers, defining constants, or performing other initialization actions.

In pre-Python 3.3 versions, __init__.py files were mandatory for creating packages. However, with the introduction of namespace packages in Python 3.3, it became possible to create packages without the need for an __init__.py file. Namespace packages, unlike regular packages, do not have a directory structure on the file system and are purely defined in code.

For more information and an example of a regular package with an __init__.py file, refer to the Python documentation at the link provided in the given answer.

The above is the detailed content of What is the Purpose of `__init__.py` in Python Packages?. For more information, please follow other related articles on the PHP Chinese website!