python:构造函数参数表示法

我学习python几个月了.在浏览金字塔教程后,我无法理解init .py中的一行

from pyramid.config import Configurator
from sqlalchemy import engine_from_config

from .models import (
    DBSession,
    Base,
    )



def main(global_config, **settings):
    """ This function returns a Pyramid WSGI application.
    """
    engine = engine_from_config(settings, 'sqlalchemy.')
    DBSession.configure(bind=engine)
    Base.metadata.bind = engine
    config = Configurator(settings=settings)
    config.include('pyramid_chameleon')
    config.add_static_view('static', 'static', cache_max_age=3600)
    config.add_route('home', '/')
    config.scan()
    return config.make_wsgi_app()

我在配置器参数中丢失了settings = settings.

这个告诉python是什么？