PySerial only working from interactive python, not from script in windows

[leonhardpetzel]

Hello,

I found a really strange issue on Windows 10 Pro using python 3.12.1 with PySerial 3.5.

I have an arduino board with MEGA2560 connected via USB and the firmware on the board will reply to a "*IDN?\r" command with some version string.

If I send the commands in an interactive python promt, all works fine:

Also from the debug console (in VS Code) all works fine:

However, when I run the commands from a script, it seems like nothing is sent to the board:

I tried to put time.sleep() everywhere, but it did not change anything. It really seems like the difference is, if the call comes from an interactive session, or not.

I am not sure, if the issue originates from PySerial, from python or from Windows.
Does somebody here have an idea, where this could come from?

Thanks and BR

[paratim]

Yes, I'm seeing an issue similar to yours. In my case a sleep(5) after the serial port creation seemed to be a workaround.

[leonhardpetzel]

Yes, I'm seeing an issue similar to yours. In my case a sleep(5) after the serial port creation seemed to be a workaround.

Thanks for the information! A 2 second sleep works for me. Amazing! I only tried 100ms sleep, which I thought was super long, but apparently not enough.

I also found that writing to the .timeout member is a very bad idea. As soon as I try to change the timeout, the next send transaction just sends garbage.