Wait for subprocess to print something to stdout, with Popen

Question

I want to make a wrapper around an existing program to create a programmable interface. The idea is that I want to expose functions that will send the appropriate input to the subprocess, and return a value corresponding to the input of that process.

However, I don't know how to make my interface wait for the program to return something.

This is what I've done.

class ProcessWrapper:
    def __init__(self, process):
        self.proc = process
    def communicate(self, message):
        self.proc.stdin.write(message)
        while True:
            result = self.proc.stdout.readlines()
            if result: return result

But this seems very ressource-demanding. Is there a better way?

Answer 1

readlines is a non-blocking function, meaning the loop will execute as fast as possible, instead of waiting for some output from the process.

What should be used here instead is readline, essentially the same function but blocking.

    def communicate(self, message):
        self.proc.stdin.send(message)
        return self.proc.stdout.readline()