code: def append_data(file_strings, file_fmt, tag):
      
      # Determine the right appending routine for the file type
      if file_fmt.lower() == "csv":
          return append_csv_data(file_strings)
      else:
          return append_ascii_data(file_strings, tag)
docs: Load the SuperMAG files
  
      Parameters
      -----------
      file_strings : array-like
          Lists or arrays of strings, where each string contains one file of data
      file_fmt : str
          String denoting file type (ascii or csv)
      tag : string
          String denoting the type of file to load, accepted values are 'indices',
          'all', 'stations', and '' (for only magnetometer data)
  
      Returns
      -------
      out_string : string
          String with all data, ready for output to a file