Python串口PermissionError 13求助：重复运行报错需重插USB

报错信息 #

serial.serialutil.SerialException: Cannot configure port, something went wrong. Original message: PermissionError(13, '无法访问端口，权限不足。', None, 31)

问题场景 #

首次插入USB后运行代码无异常，重复运行时触发上述权限错误，每次运行需重新插拔USB，已安装CH340驱动。

现有代码 #

import serial
import time

ser = None  # Initialize ser

try:
    ser = serial.Serial(
        port="COM4",  # Update this to the serial port of your device
        baudrate=9600,  # Update this according to your device's settings
        timeout=1,
        stopbits=1,
    )

    # Check if the serial port is open
    if ser.isOpen():
        print("Serial port is open")
    else:
        print("Error opening serial port")
        exit()

    # Send a SCPI command to query the voltage
    ser.write(b"VOLT 7\n")

    # Give the device some time to respond
    time.sleep(1)

    # Read the response
    response = ser.readline().decode().strip()
    print(f"Voltage: {response}")

finally:
    if ser is not None:  # Check if ser is not None before attempting to close it
        ser.close()

排查与解决方法 #

• 端口资源未完全释放：虽然代码用finally块关闭了端口，但操作系统可能存在延迟释放的情况。可以修改finally块，显式置空串口对象并添加短暂延迟：

  finally:
      if ser is not None:
          ser.close()
          ser = None  # 帮助垃圾回收器回收资源
          time.sleep(0.5)  # 给系统留足端口释放时间
  

• 进程占用或权限不足：
  • 打开任务管理器，排查是否有其他程序（如串口调试工具）占用了COM4端口，关闭后重试
  • 打开设备管理器，找到对应COM端口→右键属性→安全，确保当前用户拥有「读取/写入」权限
• 驱动兼容性问题：卸载现有CH340驱动，重新安装官方最新版本，避免老旧驱动导致的端口异常
• 改用上下文管理器优化代码：使用with语句自动管理串口资源，比手动close()更可靠，代码块结束后会自动释放端口：

  import serial
  import time
  
  try:
      with serial.Serial(
          port="COM4",
          baudrate=9600,
          timeout=1,
          stopbits=1,
      ) as ser:
          print("Serial port is open")
          ser.write(b"VOLT 7\n")
          time.sleep(1)
          response = ser.readline().decode().strip()
          print(f"Voltage: {response}")
  except serial.SerialException as e:
      print(f"串口操作错误: {e}")
  

内容的提问来源于stack exchange，提问作者zh y