python循环只在上打印值

Question

下面是一小段python代码。。它是用来读取光或暗的传感器。我想它做什么，当值下降到低于500打印“轻”和当它高于500打印“暗”。这很管用，但每次阅读都要重复课文。。而我只想在一个改变的时候打印出来。。有人知道怎么做吗？我做了不少shell编程。。但不知怎么的，这个简单的问题我无法用python完成。。在

#!/usr/bin/python

import RPi.GPIO as GPIO, time

GPIO.setmode(GPIO.BCM)

# Define function to measure charge time
def RCtime (PiPin):
  measurement = 0
  # Discharge capacitor
  GPIO.setup(PiPin, GPIO.OUT)
  GPIO.output(PiPin, GPIO.LOW)
  time.sleep(0.1)

  GPIO.setup(PiPin, GPIO.IN)
  # Count loops until voltage across
  # capacitor reads high on GPIO

  last = 9
  while (GPIO.input(PiPin) == GPIO.LOW):
    measurement += 1

  if measurement < 500:
     print last
     if last == 0:
      print "light"
      last = 1
  if measurement >500:
   print "dark"
   last = 0
   print last
  return measurement

# Main program loop
while True:
  print RCtime(4) # Measure timing using GPIO4

Answer 1

我使用一个名为readings的列表模拟传感器的读数，其余代码可以直接转换为您的用例

readings = [ 600, 600, 550, 501, 450, 400, 400, 460, 520, 600, 600]
dark = None

for i, reading in enumerate(readings):
    dark_now = 'Dark' if reading < 500 else 'Light'
    if dark_now != dark:
        dark = dark_now
        print i, reading, dark

输出

^{pr2}$