import RPi.GPIO as GPIO, time
progName="Test_isTrueIfDark.py"
print("always works with 2 diff. CD in series (covering both). ")
print("works with 1 CD sometimes. ")
print("from phys pin 38 (as input with PUD_DOWN)")
print("  to phys pin 40 (as output High).") 
GPIO.setmode(GPIO.BCM)  #BroadCoM numbering eg GPIO #s
PIN=20      #phys pin 38
PINout=21   #phys pin 40
GPIO.setup(PIN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
# on a Raspberry Pi, PullUpDown is a 10k resistor
# a photoresist photocell (CD) when lit is 5k.
GPIO.setup(PINout,GPIO.OUT)
GPIO.output(PINout, True)
print("turn phys pin 40 On")
GPIO.setup(PIN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
def isTrueIfDark(PIN):
    #Purpose: to return True if both CDs are covered
    #By: D@CC on 2023JOct29
    #Tested
    reading=GPIO.input(PIN)
    if reading:                                                                                                                                                                                                    
        state=False
    else:
        state=True
    #if end
    #time.sleep(1)
    return state
#def end
while True:
    if isTrueIfDark(PIN):
        print("Dark")
    else:
        print("Light")
    #if end
    time.sleep(1)
#while end