Packages

Packages allow you to organise your modules in an intuitive way.

__init__.py

To initialise a package, a folder has to contain the file __init__.py. This tells python that the folder is a package. __init__.py can be an empty file, or it can contain additional information to do with initalisation, or for example __all__, below.

__all__ and import * behaviour

Defining an __all__ variable insite of __init__.py defines the submodules and subpackages that should be imported if the wildcard is used. For example, if in package you have

__all__ = ["subpackage_one", "subpackage_two"]

then when you run

import package

you will have access to subpackage_one and subpackage_two.

If you don't include an __all__ variable, then importing package will mean that you have to call package.subpackage_one to access the modules of subpackage_one

Sub-packages

A package folder can contain sub-folders which can themselves contain the __init__.py file which makes them into packages. This allows you to next packages and then import them like this: package_one.package_two