Setting an exclusive lock on a file

[Eugene Perederey]

Hi all,
I want to set an exclusive lock on a file so other processes wouldn't
be able to write to it.
So I write

import fcntl
fd=open('myfile','w')
fcntl.lockf(fd, fcntl.LOCK_EX)
fd.write('some bytes')
fd.close()

But it turns out that my script doesn't write anything to file whereas
other processes do. What's wrong in my code?

-- 
Sincerely yours, Eugene Perederey