如何连续运行可以从节点接收命令的Python脚本

Question

I have set up a Raspberry Pi connected to an LED strip which is controllable from my phone via a Node server I have running on the RasPi. It triggers a simple python script that sets a colour.

I'm looking to expand the functionality such that I have a python script continuously running and I can send colours to it that it will consume the new colour and display both the old and new colour side by side. Ie the python script can receive commands and manage state.

I've looked into whether to use a simple loop or a deamon for this but I don't understand how to both run a script continuously and receive the new commands.

Is it better to keep state in the Node server and keep sending a lot of simple commands to a basic python script or to write a more involved python script that can receive few simpler commands and continuously update the lights?

Answer 1

IIUC, you don't necessarily need to have the python script running continuously. It just needs to store state, and you can do this by writing the state to a file. The script can then just read the last state file at startup, decide what to do from thereon, perform action, then update the state file.

In case you do want to actually run the script continuously though, you need a way to accept the commands. The simplest way for a daemon to accept command is probably through signal, you can use custom signal eg SIGUSR1 and SIGUSR2 to send and receive these notifications. These may be sufficient if your daemon only need to accept very simple request.

For more complex request where you need to actually accept messages, you can listen to a Unix socket or listen to a TCP socket. The socket module in the standard library can help you with that. If you want to build a more complex command server, then you may even want to consider running a full HTTP server, though this looks overkill for the current situation.

Is it better to keep state in the Node server and keep sending a lot of simple commands to a basic python script or to write a more involved python script that can receive few simpler commands and continuously update the lights?

There's no straightforward answer to that. It depends on case by case basis, how complex the state is, how frequently you need to change colour, how familiar you are with the languages, etc.

Answer 2

Another option is to have the Node app, calll the Python script as a child process, and pass to it any needed vars, and you can read python's out put as well, like so:

 var exec = require('child_process').exec;
 var child = exec('python file.py var1 var2', function (error, stdout, stderr) {
 }