code: def set_root_path(self, root_path=None, settings_module=None):
          
          if root_path:
              self.root_path = root_path
              return
  
          if settings_module:
              self.root_path = os.path.dirname(os.path.abspath(settings_module.__file__))
              return
  
          # try to guess which module import app.py
          import inspect
  
          caller = inspect.stack()[1]
          caller_module = inspect.getmodule(caller[0])
          assert hasattr(caller_module, '__file__'), 'Caller module %s should have __file__ attr' % caller_module
          self.root_path = os.path.dirname(os.path.abspath(caller_module.__file__))
docs: root_path will only be used for 3 situations:
          1. fix ``static_path`` and ``template_path``
          2. check project's directory name with the value in settings.PROJECT
          3. append parent path to sys.path