Setup

First, install the Python module.

pip install python-arduino

Next, plug in an Arduino board. Locate the device file that corresponds to it:

user@comp:~$ cd /dev

user@comp:/dev$ ll | grep ttyACM
crw-rw----   1 root    dialout 166,    0 Nov  6 00:00 ttyACM0   # This is the device file

user@comp:/dev$ sudo chmod 666 ttyACM0   # Allow all users to control it

Before you can control the board, compile and upload the Firmata program to it. Open the Arduino IDE and open File >> Examples >> Firmata >> StandardFirmata, and compile and upload.