modfl.py

import fcntl
def modfl(fd, flags):
	'''Adds all given positive flags to, and removes all given negative flags from, the given file descriptor'''
	# e.g.: modfl(f, (+os.O_SYNC, -os.O_NONBLOCK))
	# would make f synchronous and blocking

	#OR-in positive flags; NAND-out negative ones
	ins = lambda fl, x: (fl | x) if x >= 0 else (fl &~ -x)

	# 1. Get the current flag field
	cur = fcntl.fcntl(fd,fcntl.F_GETFL)
	# 2. Calculate the new flag field
	new = reduce(ins, flags, cur)
	# 3. Apply the new flag field
	return fcntl.fcntl(fd, fcntl.F_SETFL, new)