Python 2.7全局变量？

Question

我有一些试图写入套接字(ardSocket)的代码，如果它抛出异常，它将尝试重新连接。我将套接字变量声明为全局变量，以便在单独的函数中赋值时，程序的其余部分仍然可以访问它，但由于某种原因，仍然会抛出异常。当我在代码的开头全局声明实际的套接字时，一切都很正常。为什么我不能全局声明ardSocket=None，然后将其分配给一个单独的函数使用？

#!/usr/bin/env python
'''
Arduino LED values: 0=down, 1=up, 2=blink
'''
import os
from subprocess import Popen, PIPE, STDOUT
import serial
import time

ardSocket = None

def ardConnect():
    arduinoFound=False

    while arduinoFound==False:
        try:
            ardSocket=serial.Serial('/dev/ttyUSB0',9600)
            arduinoFound=True
            print "Arduino connected"
        except:
            print "Arduino not found. retrying in 10 seconds"
            time.sleep(10)

while 1==1:
    response=Popen(['ping','-c 1','google.com'],stdout=PIPE,stderr=STDOUT)
    stdout,nothing=response.communicate()

    if "Name or service not known" in stdout:               #If DNS fails
        try:
            ardSocket.write('0')                                #Solid RED LED
        except:
            ardConnect()

    else:
        pingTestArray=stdout.splitlines()                   #Split ping output into array by lines
        pingTestArrayList=pingTestArray[4].split(" ")       #Split the line containing packet loss by words
        packetLoss=pingTestArrayList[5].replace('%','')     #Remove the % from the element containing packet loss number
                                                            #and assign value to packetLoss var


        if int(packetLoss) > 30 and int(packetLoss) < 95:   #If packet loss > 30% && < 95% warn, FLASH RED LED
            try:
                ardSocket.write('2')
            except:
                print "ard error"
                ardConnect()
        elif int(packetLoss) > 94:                          #Network is down, >95% packet loss, SOLID RED LED
            try:
                ardSocket.write('0')
            except:
                print "ard error"
                ardConnect()
        else:
            try:
                ardSocket.write('1')                            #Else show good, GREEN LED
            except:
                print "ard error"
                ardConnect()
    time.sleep(5)