code: def _parse_standard_flag(read_buffer, mask_length):
      
      # The mask length tells us the format string to use when unpacking
      # from the buffer read from file.
      mask_format = {1: 'B', 2: 'H', 4: 'I'}[mask_length]
  
      num_standard_flags, = struct.unpack_from('>H', read_buffer, offset=0)
  
      # Read in standard flags and standard masks.  Each standard flag should
      # be two bytes, but the standard mask flag is as long as specified by
      # the mask length.
      fmt = '>' + ('H' + mask_format) * num_standard_flags
      data = struct.unpack_from(fmt, read_buffer, offset=2)
  
      standard_flag = data[0:num_standard_flags * 2:2]
      standard_mask = data[1:num_standard_flags * 2:2]
  
      return standard_flag, standard_mask
docs: Construct standard flag, standard mask data from the file.
  
      Specifically working on Reader Requirements box.
  
      Parameters
      ----------
      fptr : file object
          File object for JP2K file.
      mask_length : int
          Length of standard mask flag