python Non-block read file -

i want read file non-block mode. did below

import fcntl import os  fd = open("./filename", "r") flag = fcntl.fcntl(fd.fileno(), fcntl.f_getfd) fcntl.fcntl(fd, fcntl.f_setfd, flag | os.o_nonblock) flag = fcntl.fcntl(fd, fcntl.f_getfd) if flag & os.o_nonblock:     print "o_nonblock!!" 

but value flag still represents 0. why..? think should changed according os.o_nonblock

and of course, if call fd.read(), blocked @ read().

o_nonblock status flag, not descriptor flag. therefore use f_setfl set file status flags, not f_setfd, setting file descriptor flags.

also, sure pass integer file descriptor first argument fcntl.fcntl, not python file object. use

f = open("/tmp/out", "r") fd = f.fileno() fcntl.fcntl(fd, fcntl.f_setfl, flag | os.o_nonblock) 

rather than

fd = open("/tmp/out", "r") ... fcntl.fcntl(fd, fcntl.f_setfd, flag | os.o_nonblock) flag = fcntl.fcntl(fd, fcntl.f_getfd) 

---

import fcntl import os  open("/tmp/out", "r") f:     fd = f.fileno()     flag = fcntl.fcntl(fd, fcntl.f_getfl)     fcntl.fcntl(fd, fcntl.f_setfl, flag | os.o_nonblock)     flag = fcntl.fcntl(fd, fcntl.f_getfl)     if flag & os.o_nonblock:         print "o_nonblock!!" 

prints

o_nonblock!!