This line of code is calling the constructor of the parent class (in this case, the "User" class) and passing in the "api_root_url" parameter along with any additional keyword arguments (**kwargs) that were passed in.

The purpose of calling the parent constructor is to initialize any attributes or methods that are defined in the parent class and that the child class (in this case, the class that is inheriting from "User") needs in order to function properly.

By passing in the "api_root_url" parameter, the child class is able to set the value of this attribute in the parent class, which may be used by other methods or functions defined in the parent class. The **kwargs parameter allows for additional keyword arguments to be passed in and handled by the parent constructor, if needed.