Please add a constant for O_NOATIME to the os module.

 -- Macro: int O_NOATIME
     If this bit is set, `read' will not update the 
     access time of the file.  *Note File Times::.  This 
     is used by programs that do backups, so that backing 
     a file up does not count as reading it. Only the 
     owner of the file or the superuser may use this bit.

and possibly even a new character to the 'mode' paramter of the builtin 'open' function to do the same thing.