code: def __init__(self, missing_files):
      assert len(missing_files) > 0
  
      source = "source"
      if len(missing_files) > 1:
          source += "s"
  
      msg = "missing data '{}': {}".format(
          source, ", ".join(missing_files)
      )
      super().__init__(msg)
  
imports: from dvc.exceptions import DvcException
label_desc: Use image node_id 1 to create a new MissingDataSource object from inherited base classes: DvcException with example: obj = MissingDataSource(missing_files)