from __future__ import print_function
import os
with open('@test', 'w') as fid:
    fid.write('a' *100)
fid.close()
fd = os.open('@test', os.O_RDONLY)
try:
    fd2 = os.fdopen(fd, 'w')
    n = fd2.write('bbb')
    print('wrote %d to a read-only file' % n)
    # But it didn't really write ...
except Exception as e:
    print('properly raised %r' % e)
else:
    print('should raise, opening a ro descriptor for writing')
try:
    os.close(fd)
except:
    print('should not raise, fd remains open throughout')
with open('@test') as fid:
    # even though fd2 claimed to write, the contents remain unchanged
    print(fid.read())
os.unlink('@test')