Understanding os.fork and Queue.Queue

The POSIX fork system call creates a new process, rather than a new thread inside the same adress space:

The fork() function shall create a new process. The new process (child process) shall be an exact copy of the calling process (parent process) except as detailed below: [...]

So the Queue is duplicated in your first example, rather than shared between the parent and child.

You can use multiprocessing.Queue instead or just use threads like in your second example :)

By the way, using list comprehensions just for side effects isn't good practice for several reasons. You should use a for loop instead:

for x in range(10): q.put(x)

To share the data between unrelated processes, you can use named pipes. Through the os.open() funcion..http://docs.python.org/2/library/os.html#os.open. You can simply name a pipe as named_pipe='my_pipe' and in a different python programs use os.open(named_pipe, ), where mode is WRONLY and so on. After that you'll make a FIFO to write into the pipe. Don't forget to close the pipe and catch exceptions..

Fork creates a new process. The child and parent processes do not share the same Queue: that's why the elements put by the parent process cannot be retrieved by the child.