Extra line generated when writing serial data to file using pyserial

Question

I am reading a string from the serial port using pySerial and then writing data to a file with a time stamp. For some reason a new line is written with an empty data entry ( with the time stamp) every time I connect the serial port. I have set the write to file as append so that every time I read data from the port I can use the same file. Is there anything fundamental that I am missing in setting up the serial port? I have attached the code and the output written in the file. Thanks a lot!

sPrt = serial.Serial( port = 5, baudrate = 9600 , bytesize = 8 )
sPrt.flushInput()

while True:
        data = sPrt.readline().decode('utf-8')[:-2]
        print(data)
        dateTimeObj = datetime.now()
        timeStamp = dateTimeObj.strftime("%d-%b-%Y %H:%M")
        with open(fileName,"ab") as f:
                writer = csv.writer(f,delimiter=",")
                writer.writerow([timeStamp,data])

and the output in the file is: Here I started data logging at 14:43, disconnected the port after two data points and then connected it again at 14.44. Each time a new connection was made a line without any data got added to the saved file

16-Nov-2022 14:43,
16-Nov-2022 14:43,"A"
16-Nov-2022 14:43,"B"
16-Nov-2022 14:44,
16-Nov-2022 14:44,"A"

The output of the print(data) line is:

A
B

A

I tried to check if the data variable is a "\n" and to only write to file if it isnt but that did not seem to do anything .

Answer 1

I don't see the problem here, apparently data is either something like 'A' (no newline) or '' (no newline, just an empty string). In either case, .writerow() will write a full row, followed by a newline.

If you don't want newlines written to the output file:

with open(fileName, "a", newline='') as f:
    ...

I don't see it working with "ab" anyway, since the csv.writer expects to be writing to a text file, not a binary one. As do you apparently, since you called .decode()