Once you close the IDE, you may have to a) reset the Arduino or b) remove and replace the USB cable between the PC and Arduino.

Just out of curiosity, how are you powering the UNO?

 

Once you close the IDE, you may have to a) reset the Arduino or b) remove and replace the USB cable between the PC and Arduino.

Just out of curiosity, how are you powering the UNO?

With the usb cable, but on some other projects I use a 9V b
attery

 

With the usb cable, but on some other projects I use a 9V b
attery

Have you tried my suggestions?

The Windows USB driver for the Arduino has its issues. Sometimes you need to reload it. Option b will do that. Option a might reset it.

 

Have you tried my suggestions?

The Windows USB driver for the Arduino has its issues. Sometimes you need to reload it. Option b will do that. Option a might reset it.

I tried it, but nothing is working, I also tried connected a smaller program to Arduino, that just sends a number, and if i first start python i don't get the error, but than nothing is showing up on Arduino(I also can't use Serial monitor than), so I tried to display the number on a LCD display, but nothing was showing up.

 

Nothing is working...

You have three things to solve. Get them working one at a time independent of the others.

1) PC USB COM port configure
2) Python code
3) Arduino code

 

Nothing is working...

You have three things to solve. Get them working one at a time independent of the others.

1) PC USB COM port configure
2) Python code
3) Arduino code

ok, I will try fixing the code

 

I tried it, but nothing is working, I also tried connected a smaller program to Arduino, that just sends a number, and if i first start python i don't get the error, but than nothing is showing up on Arduino(I also can't use Serial monitor than), so I tried to display the number on a LCD display, but nothing was showing up.

Now you’ve introduced another issue... you’ll never figure this out this way...

I’ve been following MrChips’ advice in my replies to you. Trying to address his first point.

Write simple test programs. Send an “A” from Python to the Arduino and illuminate the built-in Arduino led when it’s received. No worries if your LCD is working. Simple programs that are likely to work.

Otherwise, proceed as MrChips suggests.

 

Now you’ve introduced another issue... you’ll never figure this out this way...

I’ve been following MrChips’ advice in my replies to you. Trying to address his first point.

Write simple test programs. Send an “A” from Python to the Arduino and illuminate the built-in Arduino led when it’s received. No worries if your LCD is working. Simple programs that are likely to work.

Otherwise, proceed as MrChips suggests.

Ok , I will try, thanks