def out_of_date(original, derived):
 return ((not os.path.exists(derived)) or (os.path.exists(original) and (os.stat(derived).st_mtime < os.stat(original).st_mtime)))

def out_of_date ( original , derived ) : return ( ( not os . path . exists ( derived ) ) or ( os . path . exists ( original ) and ( os . stat ( derived ) . st_mtime < os . stat ( original ) . st_mtime ) ) )
returns true if derivative is out-of-date wrt original .