The GPIO pin charts below are for the Raspberry Pi 3 Model B V1.2
You have a choice of two numbering systems in Python. Import the
import RPi.GPIO as IOIO.setmode(GPIO.BOARD)
import RPi.GPIO as IOIO.setmode(GPIO.BCM)
GPIO.BOARD mode uses the numbers in the gray rectangles from 1 to 40.
GPIO.BCM refers to the pins by the "Broadcom SOC channel" number.These are the numbers after the "GPIO" in the coloured rectangles. These numbers changed between model B versions of the Raspberry Pi.
It is safer if you use
GPIO.BOARD numbers in your Python programs, especially if you have an older Raspberry Pi model.
For general input output circuits we suggest you only use the pins with the orange outline around the grey boxes.