Why is my Python serial write command giving a TypeError?

General Discussions
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1

I’m using Python 3.3 and pySerial for serial communication, but when I try to write a command to my COM port using the write() method, it doesn’t accept my string. I’m encountering the following error:

Error at ser.write("%01#RDD0010000107**\r") with Traceback like this:
data = to_bytes(data)
b.append(item)
TypeError: an integer is required.

Here’s the code I am using:

import time
import serial

ser = serial.Serial(
    port='\\\\.\\COM4',
    baudrate=115200,
    parity=serial.PARITY_ODD,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)

if ser.isOpen():
    ser.close()
ser.open()
ser.isOpen()

ser.write("%01#RDD0010000107**\r")
out = ''
# Let's wait one second before reading output to give the device time to respond
time.sleep(1)

while ser.inWaiting() > 0:
    out += ser.read(40)

if out != '':
    print(">>" + out)

ser.close()

What could be the cause of the error, and how can I resolve it in the context of Python serial write?

2

From my experience with python serial write, I found that the problem was due to the string needing to be converted into a bytearray. To fix this, I modified my code like this:

ser.write("%01#RDD0010000107**\r".encode())

This change resolved the error and allowed me to send the string to the serial port correctly. Always remember to check the data type before sending it out!

3

Ah, yes, that’s one way to go about it. What I usually do is use bytes() to convert the string into a byte object before writing it. Here’s an example:

ser.write(bytes("%01#RDD0010000107**\r", 'utf-8'))

In fact, this method can be especially useful when you’re working with specific encodings like UTF-8. I’ve found it to be very reliable when dealing with python serial write issues, especially when the encoding matters.

4

Totally agree with both of you! Another approach I’ve found useful, especially when working with simpler encodings, is to explicitly use str.encode() with a specific encoding. For example:

ser.write("%01#RDD0010000107**\r".encode('ascii'))

This ensures that your data is encoded in the right format for the serial communication. It’s something I always do when troubleshooting python serial write errors. It’s also great for ensuring compatibility across different systems!