code: def _integer_to_timestamp(arg, unit='s'):
      
      op = ops.TimestampFromUNIX(arg, unit)
      return op.to_expr()
docs: Convert integer UNIX timestamp (at some resolution) to a timestamp type
  
      Parameters
      ----------
      unit : {'s', 'ms', 'us'}
        Second (s), millisecond (ms), or microsecond (us) resolution
  
      Returns
      -------
      timestamp : timestamp value expression