擅长:python、mysql、java
<p>我想出来了。虽然要定义的变量保留全局范围,但需要在函数内部单独声明它属于全局范围。“global”命令不能在函数之外。在</p>
<pre class="lang-html prettyprint-override"><code>import RPi.GPIO as GPIO
import time, sys
LIQUID_FLOW_SENSOR = 32
GPIO.setmode(GPIO.BOARD)
GPIO.setup(LIQUID_FLOW_SENSOR, GPIO.IN, pull_up_down = GPIO.PUD_UP)
rotation = 0
def countPulse(channel):
global rotation
rotation = rotation+1
print ("Total rotation = "+str(rotation))
litre = rotation / (60 * 7.5)
two_decimal = round(litre,3)
print("Total consumed = "+str(two_decimal)+" Litres")
GPIO.add_event_detect(LIQUID_FLOW_SENSOR, GPIO.FALLING, callback=countPulse)
while True:
try:
time.sleep(1)
except KeyboardInterrupt:
print 'Program terminated, Keyboard interrupt'
GPIO.cleanup()
sys.exit()
</code></pre>