Mon 22 August 2016
If you need to quickly use a serial port, use pyserial:
python -m serial.tools.miniterm -e /dev/tty.usbserial-A5004Flb 9600
This opens up a simple little terminal. The -e echos what you type. The above serial port is on macOS, but RPi typically has /dev/ttyACM0 for the serial port.
Depending, if you don't have permission to open the serial port and are forced to use sudo, add your user to the tty group:
sudo usermod -a -G tty pi
Also, the RPi typically connects the serial port to a login terminal. Use raspi-config to turn that off, then reboot.
Also you might have to edit /boot/config.txt and add enable_uart=1 for the RPi3.