Question

我正在尝试创建一个每1秒递增一个变量的线程计时器。该变量位于回调函数中，并在串行接收函数中查询，以便在规定时间内未收到数据时设置超时。回调函数以及接收函数都将变量声明为全局变量，并将变量声明为在定时器类之外声明。每当触发回调时，都会显示分配错误。不确定我做错了什么来修复此错误。

# python27 Serial Interface Prototype - MH 20170711
__author__ = 'MHammersley'

from serial import *
import threading

gRdTimeout = 0
t = None

class Cmd_Resp(object):

    # opens a usb-to-serial com port session at the specified baud rate
    def __init__(self, serial_port, baud, delimiter = '/n'):
        #ensure non-blocking
        self.serial_port = serial_port
        self.baud = baud
        self.delimiter = delimiter
        self.port = Serial(serial_port, baud, timeout = 0, writeTimeout=0)
        global t
        self.t = threading.Timer(1.0, self.UpdateTimer).start()

    # this function updates the timer variable in 1 second increments
    def UpdateTimer(self):
        global gRdTimeout
        gRdTimeOut += 1
        print('Count: ', gRdTimeout)

    def start(self):
        global t
        self.t.start() # start the timer

    # write only command, no read response
    def send(self, cmd):
        #Write command to com port
        self.port.write(cmd+self.delimiter)

    # read only until the expected response string is received
    def receive(self, exp_resp, timeout):
        #Read device response from com port.
        global gRdTimeout, t 
        gRdTimeOut = 0 # set the timeout count to 0
        serBuffer = "" # empty the buffer
        tflag = True
        self.t.start() # start the timer
        loop = True
        while (loop != False):
            c = self.port.read()
            if c == '\n':
                serBuffer += "\n" # add the newline to the buffer
            else:
                serBuffer += c # add to the buffer
            if exp_resp in serBuffer:
                loop = False
            if gRdTimeout >= timeout:
                break
        self.t.cancel() # stop the timer
        return serBuffer

    # sends a command to the uut and reads until the expected response is received
    def request(self, cmd, exp_resp):
        self.send(cmd)
        self.exp_resp = exp_resp
        return self.receive(exp_resp)

Answer 1

def UpdateTimer(self):
    global gRdTimeout # lowercase O
    gRdTimeOut += 1   # capital O
    print('Count: ', gRdTimeout)

那就是说，你应该真的避免使用像这样的全局变量。特别是因为你已经把它封装成一个类的麻烦了。根据{{1}}致电receive时设置超时最长值，然后在每次检查时查看datetime.datetime.now() + datetime.timedelta(seconds=timeout)是否早于或晚于截止值。

datetime.datetime.now()

获取Python之前赋值错误之前引用的局部变量

1 个答案: