import errno
import os
import fcntl

try:
    _MAXFD = os.sysconf("SC_OPEN_MAX")
except:
    _MAXFD = 256

def isopen(fd):
    try:
        fcntl.fcntl(fd, fcntl.F_GETFD, 0)
    except IOError as e:
        if e.errno == errno.EBADF:
            return False
        raise
    return True

if __name__ == "__main__":
    print(','.join(str(fd) for fd in range(0, _MAXFD) if isopen(fd)))