code: def write(config):
          
          root = config
          while root._parent:
              root = root._parent
  
          for source in root._sources:
              if source.writable and source.dirty:
                  source.save()
docs: Commits any pending modifications, ie save a configuration file if
          it has been marked "dirty" as a result of an normal
          assignment. The modifications are written to the first
          writable source in this config object.
  
          .. note::
  
             This is a static method, ie not a method on any object
             instance. This is because all attribute access on a
             LayeredConfig object is meant to retrieve configuration
             settings.
  
          :param config: The configuration object to save
          :type  config: layeredconfig.LayeredConfig