python - pySerial-UnboundLocalError : local variable 'serial_port' referenced before assignment

Question

我得到这个程序来保存控制台从 USB 连接设备(无线传感器)打印的日志文件。它产生错误:

UnboundLocalError: local variable 'serial_port' referenced before assignment.

它是经过修改的 pySerial.py 以满足我的应用程序的需求。它记录控制台打印内容的一部分(最好我想记录所有内容)

我对python不熟悉，所以我无法自己解决这个问题。非常欢迎您的帮助!代码哪里出错了？

import serial
import io
import time        

def serial_com():
    '''Serial communications: get a response'''
    # open serial port
    try:
        serial_port = serial.Serial('/dev/ttyUSB0', baudrate=115200, timeout=1)
    except serial.SerialException as e:
        print("could not open serial port '{}': {}".format('/dev/ttyUSB0', e))

    # read response from serial port
    lines = []
    while True:
        lines = []
        line = serial_port.readline()
        lines = ([time.localtime().tm_hour, 
                  time.localtime().tm_min,
                  time.localtime().tm_sec,
                  line.decode('utf-8').rstrip()])

        # wait for new data after each line
        timeout = time.time() + 10
        while not serial_port.inWaiting() and timeout > time.time():
            pass 
        if not serial_port.inWaiting():
            break 

    #close the serial port
    serial_port.close()

    linesplit = str(lines[3]).split()
    temp1 = -40+0.01*float(linesplit[2])
    output = [lines[0], lines[1], lines[2], temp1]
    return output

def writeXML(lines):
    from xml.etree.ElementTree import Element, SubElement, tostring, ElementTree
    root = Element('CATALOG')
    child1 = SubElement(root, 'Measurement')
    child11 = SubElement(child1, 'Time')
    child11.text = str(lines[0])+':'+str(lines[1])+':'+str(lines[2])
    child12 = SubElement(child1, 'Values')
    child12.text = str(round(lines[3], 2))
    tree = ElementTree(root)
    tree.write('/var/www/values.xml', 'UTF-8')

while True:
  lines=serial_com()
  writeXML(lines)
  time.sleep(10)

Answer 1

当你遇到异常时，你需要退出你的函数:

try:
    serial_port = serial.Serial('/dev/ttyUSB0', baudrate=115200, timeout=1)
except serial.SerialException as e:
    print("could not open serial port '{}': {}".format('/dev/ttyUSB0', e))
    return

因为如果您确实收到异常，则永远不会设置 serial_port ，从而导致 UnboundLocalError 异常。

我在这里使用return作为示例；无论哪种方式你的脚本都会中断。您可能应该重新引发异常，或返回合适的默认值。