PySerial App runs in shell, by not py script

Question

I have a very simple python script that uses pySerial to send data over the serial port to my arduino. When I execute this line-by-line in the python shell, it works just fine, but when I put it in a ".py" file, and try to run it, nothing happens. Though the Serial lights on my UART do flash. So something is getting through, but it's garbage (I checked).

Here is the simple code.

import serial

ser = serial.Serial('COM3',9600,timeout=.2)
ser.write('A')
ser.close()

I've already tried adding sleeps, but nothing seems to be fixing it. Any ideas?

Answer 1

show how you run it? take note not to name your python script as serial.py. Are you on *nix or Windows?

Answer 2

Maybe be stupid, but try to type only "myscript.py" in cmd.exe, if you are on Windows. I've noticed that on Windows, you do not need to type "python" before script name. This is of course for standard CPython installation on Windows.

Answer 3

OK, I've figured it out!

It's necessary to use code like this before performing the write:

time.sleep(1)
ser.setDTR(level=0)
time.sleep(1)

Otherwise, the arduino automatically resets upon receiving a serial connection for some reason. yay!