python run a constant subprocess in background

If you run an external command, you’ll likely want to capture the output of that command. In this case, make sure the Python binary is called python3 on your system too, and that it’s in the PATH. Perhaps, you’ll even get an error looking like this: FileNotFoundError: No such file or directory: 'python3'. Your result may vary because your Python version will likely be different. It depends on the process you called what the different return code means.Īs you can see in the output, the Python binary printed its version number on standard out, which is usually your terminal. Any other return code would mean there was some kind of error. The process returned code 0, meaning it was executed successfully.

Inspect the result variable, which is of the type CompletedProcess.

Run a subprocess, in this case the python3 binary, with one argument: -version.

> result = n()ĬompletedProcess(args=, returncode=0)

Let’s request the version of the default python3 installation on our system next: > import subprocess In fact, we can call Python, the binary, from our Python code. (a list of your directories will be printed) Let’s start with a simple call to ls, to list the current directories and files: > import subprocess Check our detailed Python installation instructions if you need help with that.

Make sure you have at least that Python version, but preferably you should be running the latest version. From this library, we’ll work with the run command. Since it is part of Python 3, you don’t need to install it separately. Create a Python subprocess with nĮnough with the theory, it’s time to get our hands dirty and write some code to execute external commands.įirst of all, you need to import the subprocess library. I thought it would be nice for you to know what’s going on internally, but if you feel confused, rest assured that you don’t need this knowledge to do what you want: running an external command with the Python subprocess module.

This wrapper is the function run() from the subprocess package and that’s what we’ll use in this article. Thanks to the wrapper, running an external command comes down to calling a function. We can go the low-level way and do much of this ourselves using the Python subprocess module, but luckily, Python also offers a wrapper that will take care of all the nitty-gritty details, and do so safely too. That copy, in turn, replaces itself with another process: the process you were looking to execute. First, the process forks itself, creating a copy. We can utilize this same technique to start another process, though. This can be useful if you want to parallelize your code and utilize multiple CPUs on your machine. The process forks itself, meaning a new copy of the process is created and started. What happens internally (inside the OS kernel) is what’s called a fork. A parent process spawning two sub-processes

Python run a constant subprocess in background