docs: def one(self, filetype, **kwargs):
          ''' Returns random one of the given type of file
  
          Parameters
          ----------
          filetype : str
              File type parameter.
  
          as_url: bool
              Boolean to return SAS urls
  
          refine: str
              Regular expression string to filter the list of files by
              before random selection
  
          Returns
          -------
          one : str
              Random file selected from the expanded list of full paths on disk.
  
          '''
          expanded_files = self.expand(filetype, **kwargs)
          isany = self.any(filetype, **kwargs)
          return choice(expanded_files) if isany else None