打开arduino的串口时出错

Question

代码如下......

import serial
import time

# # Serial port parameters
serial_speed = 9600
serial_port = ('COM26') # bluetooth shield hc-05


while True:

 if __name__ == '__main__':

    print("conecting to serial port ...")
    ser = serial.Serial(serial_port, serial_speed, timeout=1)
    input =raw_input('Enter:')
    print ("sending message to turn on PIN 13 ...")
    ser.write(input)

    print( "recieving message from arduino ...")
    data = ser.readline()

    if (data != ""):
        print ("arduino says: %s" % data)
    else:
        print ("arduino doesnt respond")

它第一次运行正常，但下次我收到错误...  SerialException：无法打开端口'COM26'：WindowsError（5，'访问被拒绝。'）

Arduino代码如下......

 void setup() {
 // initialize serial:
 Serial.begin(9600);
 // initialize the led pin
 pinMode(13, OUTPUT);
}

 void loop() {
 while (Serial.available()) {
 char inChar = (char)Serial.read();
 switch(inChar) {
   case '1':
    digitalWrite(13, HIGH);
    Serial.print("pin 13 was turn on");
    break;
   case '0':
    digitalWrite(13, LOW);
    Serial.print("pin 13 was turn off");
    break;
 }
}
}

请帮助！