Create a sort of command line for a python server

Question

I have been experimenting with Python socket servers and such. I came across an idea and I am having a hard time implementing it. I want the server side to be able to enter different commands, for starting and stopping the server, and performing various other tasks. My problem is, when I start having a lot of commands, my program ends up looking like spaghetti:

if command == "start":
    print("Starting server")
    time.sleep(1)
    listener_thread.start()
elif command == "stop":
    print("Stopping server...")
    time.sleep(1)
    listener_thread.stop()
elif command in ["q", "quit"]:
    print("Quitting server...")
    time.sleep(1)
    for t in connections:
        t.stop()
    listener_thread.stop()
    exit()
else:
    print("Invalid command")

One of my friends who has been programming for a while said I should try and use a dictionary to store a function reference for each command. I created a dictionary like this:

commands = {
    "start": cmd_start, # This would be a reference to cmd_start()
    "stop": cmd_stop, # Same here and so forth
    "quit": cmd_quit
}

And I would call these commands like this:

while True:
    command = input("enter a command: ")
    if command in commands:
        commands[command]()

The problem with this method is that sometimes I want a command with multiple arguments and sometimes I don't. I want to be able to have different commands with varying arguments, specify their required arguments, and check to make sure the command is a valid command with all the required arguments. I am new to programming, and I have tried thinking of a clean way to implement this. I found nothing useful on google so hopefully someone can assist me. Thanks.

Answer 1

If you know the commands' structure this is a task of parsing and it is up to the format. Other than that you can send variable length arguments using the star operator * (you can also send keyword arguments using ** but I'd start with this).

Here is a simple example:

command = input("enter a command: ")
arguments = input("enter arguments separated by a single space: ").split()
if command in commands:
    commands[command](*arguments)

Note than this will send all arguments as a string. This is a basic demonstration:

>>> def func_with_three_params(a, b, c):
...     print a, b, c
... 
>>> three_args = "1 2 3".split()
>>> func_with_three_params(*three_args)
1 2 3

As mentioned in the comments to your question this is a very common task and libraries do exist to parse various common formats. One which is often used (I use it as well) is argparse.