An __init__.py file is used to mark directories on disk as Python package directories.
This prevents directories with a common name, such as string, unintentionally hiding valid modules that occur later on the module search path.
Note: Having an
__init__.pyfile in a directory is not required to import modules from that directory, it will just create a Namespace Package. But it is required if you want to create a regular package. See packages and this for more information.
In the simplest case, __init__.py can just be an empty file.
It usually contains the __all__ variable, which is used to define what symbols are exported when from <package> import * is used on the package. See this for more information.