Disable the serial console, disable bluetooth and disable the hciuart service:

https://www.raspberrypi.org/documentation/configuration/uart.md https://www.raspberrypi.org/forums/viewtopic.php?t=178071

Disable hciuart and other bluetooth related services:

• systemctl disable hciuart
• systemctl disable bluealsa
• systemctl disable bluetooth

Disable serial console:

• Check /boot/cmdline.txt
• Comment line console=serial0,115200 or console=ttyAMA0,115200 or similar

Disable bluetooth

• Add dtoverlay=pi3-disable-bt to /boot/config.txt

Serial port configuration in Python:

https://pythonhosted.org/pyserial/shortintro.html#opening-serial-ports

Consider a timeout!