It's a part of a package. Here's the documentation.
__init__.pyfiles are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as
string, from unintentionally hiding valid modules that occur later (deeper) on the module search path. In the simplest case,
__init__.pycan just be an empty file, but it can also execute initialization code for the package or set the
__all__variable, described later.