PySerial [Error 5] Access is Denied

Question

I am trying to write a program in Python that will loop to keep checking the serial port (COM4) and print out a message when the character "1" is read from the serial port. I want to send "1" over the serial port from an Arduino gadget upon the push of a button.

However, I get the error "[Error 5]: Access is Denied" when I try to create an instance of a serial object. (It automatically tries to open upon instantiation, which is where the error is, from what I can see from the file in the PySerial package that handles this.)

My code:

c = serial.Serial('COM4', 9600)
while True:
    signal = c.read()
    print signal
    print "running"
    time.sleep(2)
    c.flushOutput()

It never gets past the "c = serial.Serial('COM4', 9600), though. That's where the error pops up. How can I fix this?

Answer 1

UPDATE: This is apparently no longer possible in PySerial 3.0.

Under Windows, I've always used the port=<int> approach with success.

I.e. change your code to:

c = serial.Serial(3, 9600)

Answer 2

For me the solution didn't work but what worked was closing all the applications that were interacting with the given com port.

Answer 3

For Python 2.6 use the zero-based COM port index. For Python 2.7.x you can use the full name "COM4". From my experience it's better to use the 2.7 version. Install Python 2.7.x and Setup Tools (aka Easy Install). Once you've got this, install pyserial module by typing easy_install -U pyserial (see pyserial installation doc).

Remember to add python path to PATH environmental variable.

Answer 4

Please, take care with the python versions.

From the pyserial manual about: class serial.Serial https://pyserial.readthedocs.io/en/latest/pyserial_api.html#classes

...........

The port is immediately opened on object creation, when a port is given. It is not opened when port is None and a successive call to open() is required.

port is a device name: depending on operating system. e.g. /dev/ttyUSB0 on GNU/Linux or COM3 on Windows.

............

Changed in version 3.0: numbers as port argument are no longer supported

Answer 5

that works with PORT COM N-1 in python (N is your number of COM)