import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(32, GPIO.OUT)
base=GPIO.PWM(32,10) #this defines board pin 32, gpio pin 12, and makes the PWM 10 times per second, I think
base.start(0)
base.ChangeDutyCycle(0)

...

if temp>40000:
    #set fan speed to 80%
    base.ChangeDutyCycle(80)