Getting an input/output error from python with pyserial

Question

I have a python script that writes data packets to an arduino board through pyserial. Sometimes while writing the code to the board pyserial raises an input/output error with errno 5

Some research says that this indicates an error while writing in the file representing the connection to the arduino board.

The code that sends, sends only single byte packets:

try:
    # Check if it's already a single byte
    if isinstance(byte, str):
        if len(byte) == 1: # It is. Send it.
            self.serial.write(byte)
        else: # It's not
            raise PacketException
    # Check if it's an integer
    elif isinstance(byte, int):
        self.serial.write(chr(byte)) # It is; convert it to a byte and send it
    else: raise PacketException # I don't know what this is.
except Exception as ex:
    print("Exception is: " + ex.__getitem__() + " " + ex.__str__())

The error printed by this code is:

OS Error Input/Output Error Errno 5

Is there something wrong in my code while sending. Do I need to check if the serial connection is ready to send something or should there be a delay after the sending? Or could there be a problem with the hardware or the connection with the hardware?

Edit I looked into the linux implementation from pyserial and the implementation is only passing the error to my code. So no new real insights from there. Could you think of a good way to test what is happening in the program?

Answer 1

The only issue I can immediately see in your code is an indentation problem -- change your code as follows:

try:
    # Check if it's already a single byte
    if isinstance(byte, str):
        if len(byte) == 1: # It is. Send it.
            self.serial.write(byte)
        else: # It's not
            raise PacketException
    # else, check if it's an integer
    elif isinstance(byte, int): 
        self.serial.write(chr(byte)) # It is; convert it to a byte and send it 
    else: 
        raise PacketException # I don't know what this is.
except Exception as ex:
    print("Exception is: " + ex.__getitem__() + " " + ex.__str__())

I doubt your error comes from this, but try it this way and let us know! You were checking if byte is an int only in the case in which it's a str, so the elif always failed by definition. But I think if you real code indentation had been like this, you'd have gotten a SyntaxError, so I think you just erred in posting and your real problem remains hidden.

Answer 2

If you are running this on Windows, you can't have the Arduino IDE open with a serial connection at the same time that you run your Python script. This will throw the same error.

Answer 3

Sorry to have bothered you but I'm very sure that the error is caused by the arduino resetting itself and therefore closing the connection to the computer.