Python serial read corrupting print statements

Question

I have this bizarre situation where reading from a serial port is appearing to corrupt calls to print. This code:

        ser = serial.Serial('COM13', 115200, timeout=5)
        ser.reset_input_buffer()
        ser.reset_output_buffer()

        ser.write("statn".encode('utf-8'))
        ser.flush()

        for i in range(10):
            print(f"read: <{self.ser.read(10).decode('utf-8')}>")

outputs

>ead: <s
read: <
>
read: <>
read: <>
read: <>
...

How can that first ‘>’ be printed by python the first time instead of the r of read?!

If I replace the serial calls with just a string, the behaviour is no longer seen .

Asked By: ACarter

||

Source

Answer 1

A wild guess is that you’re getting a “carriage return” character (ASCII 13) from the serial port — that would cause the terminal to jump back to the leftmost position. Try adding a !r to the end of the {} block in the f-string, so that it prints the repr of the string (or just omit the .decode(...) so that the undecoded byte array gets printed); that should make it obvious if there are any unprintables in there.

Answered By: Ture Pålsson

Python serial read corrupting print statements

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