code: def _encode_to_morse_string(message, letter_sep):
      
      def to_string(i, s):
          if i == 0 and s == ' ':
              return '  '
          return s
      return letter_sep.join([to_string(i, s) for i, s in enumerate(_encode_morse(message))])
docs: >>> message = "SOS"
      >>> _encode_to_morse_string(message, letter_sep=' '*3)
      '...   ---   ...'
  
      >>> message = " SOS"
      >>> _encode_to_morse_string(message, letter_sep=' '*3)
      '     ...   ---   ...'