'WSGI application interface'

def __call__(self, environ, start_response):

    if self.conditional_response:
        return self.conditional_response_app(environ, start_response)
    headerlist = self._abs_headerlist(environ)
    start_response(self.status, headerlist)
    if (environ['REQUEST_METHOD'] == 'HEAD'):
        return EmptyResponse(self._app_iter)
    return self._app_iter
