code: def snapshot_peek_number( fd, off ):
      
      # read number of 8 bytes 
      fd.seek( off - 8, os.SEEK_SET )
      value_hex = fd.read(8)
      if len(value_hex) != 8:
          return None
      try:
          value = int(value_hex, 16)
      except ValueError:
          return None
  
      return value
docs: Read the last 8 bytes of fd
      and interpret it as an int.