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Errors in serial data

I get errors in serial data in my python program but when I use PuTTY I get clean data without errors. I am not sure if I am writing the serial routine properly or I am missing something that introduce errors.

# Serial port config 
import serial
ser = serial.Serial("COM7", 9600)

# Send character 'A' to start the program

# Read line  
while True:
    bs = ser.readline()
    bs = bs.replace(b'\n', b' ').replace(b'\r', b' ')

# Save data in the simple text file 
    f = open("readme.txt", "a")
    f.write( "\n\n")
Hi, please post full error traceback message in error tags. It's hard to figure out what could be the issue without seeing that.
The received data has errors. Is there anything missing in the python code ? The data comes in a string every 200 ms and then 800 ms. I am not sure if traceback should have anything.

The string I should receive "Received Data is 0x88844422" but actually I get errors in the string sometime one letter is missing or corrupted and the other time the other one. This is communication error in the received string. If I use PuTTY or TeraTerm I don't see the communication error.
Ah I understand what you mean now.

I am not able to figure what could be wrong with the code. But checking this SO Q&A got me thinking, parity or stopbits settings may need to be provided at the receiving end to match the sending end.
It's been a long time since I played with serial. But I remember, sometimes I got results almost effortlessly (just modifying example codes). And sometimes I struggled a lot, thanks to some "minor" detail that made all the difference.
i had the same problems.

but in my case it was not a software issue , but a hardware issue.

i used a aliexpress serial -usb convertor ,
and when i repaired the hardware with genuine parts ( eg max232 or ftdi )
then my serial data was ok

otherwise , add delays , cos the timing of serial (baudrate ) is rather slow , compared with a python script

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