Is there a point to using a with statement for creating a stem.control.Controller object?

Question

I have some python that talks to a tor daemon, here it tells the daemon to shut down.

from stem import Signal
from stem.control import Controller

def shutDownTor():
    with Controller.from_port(port=portNum) as controller:
        controller.signal(Signal.SHUTDOWN)

I'm using a with statement because the code I'm ~~stealing from~~ learning from does so too. The code works fine, but I'm wondering if there is any point to using the with statement.

I know that when you use with to open files it makes sure the file closes even if there's an Exception or interrupt. But in this case it seems like all with is doing is adding an un-necessary tab. The variable controller is even left inside the namespace.

"The variable controller is even left inside the namespace." ? — DeepSpace, Jan 04 '20 at 19:14
Your understanding of what `with` is doing is just one very specific use case. `with` doesn't "open and close files" — DeepSpace, Jan 04 '20 at 19:15
In order to fully understand what `with` is doing *here*, one will have to read the implementation of `Controller.from_signal` — DeepSpace, Jan 04 '20 at 19:18

score 1 · Answer 1 · answered Jan 04 '20 at 19:14

If you would like to get rid of the with statement you will have to handle all of the open,close and exception on your own.

This will results with:

  try:
    controller = Controller.from_port()
  except stem.SocketError as exc:
    print("Unable to connect to tor on port 9051: %s" % exc)
    sys.exit(1)
  finally:
      controller.close()

Which results with the same and I will quote "un-necessary tab".

You can skip all of it (handle the close, open and exception) if you are aware of and ready for all the consequences of it.

score 1 · Accepted Answer · answered Jan 04 '20 at 19:16

The Controller class you import from stem is a wrapper for ControlSocket which is itself a wrapper around a socket connection to Tor protocol. So when you use with in your code, you do so to open a connection with the given port. The same way the file is open and closed, you will have to open and close the connection yourself if you want to get rid of with.

Is there a point to using a with statement for creating a stem.control.Controller object?

2 Answers2