python脚本中的反向事件触发器

Question

I have a throw switch which triggers the relevant output from the script below when open but does nothing when it is closed. I would like it to do the opposite ie it triggers the relevant output when closed but not when open but having played around with the various parameters cannot get it to do what I want.

import RPi.GPIO as GPIO
import smtplib
import time
import datetime

GPIO.setmode(GPIO.BCM)
GPIO.setup(21, GPIO.IN, pull_up_down=GPIO.PUD_UP)

# function for the door opening
def door_open():
    print datetime.datetime.now().strftime("%Y-%m-%d %H:%M")

#initialise a previous input variable to 0 (assume button not pressed last)
prev_input = 0
while True:
  #take a reading
  input = GPIO.input(21)
  #if the last reading was low and this one high, print
  if ((not prev_input) and input):
    door_open()
  #update previous input
  prev_input = input
  #slight pause to debounce
  time.sleep(0.1)

Answer 1

Have you tried putting something like this after the check for door_open() :

if (prev_input and (not input)):
    door_closed()

You'll need to implement door_closed() , of course.