SerialException: could not open port (Access is denied)

Question

I am writing Python v2.x in Windows7 OS. When I run my code, the following error happens frequently.

serial.serialutil.SerialException: could not open port 'COM4': WindowsError(5, 'Access is denied.')

Here are what I did:

1) I check device manager, COM 4 can be seen, but cannot open

2) In my code, I do close COM port after using it

3) Here is COM config in my code: ser = serial.Serial( "COM4", 9600, timeout=0.05)

4) I reboot computer, the problem is gone, but it happens again after a while

5) I wonder it is a problem related to my Python code or Windows system?

So considering above fact, could anyone help me out? Thanks and Happy New Year!

=)

Answer 1

I had Ultimaker Cura Slicer (for my 3D printer) open, and that was holding control of the COM3 port for some reason. Once I killed that app, then it (VSCode) worked fine for uploading code to my ESP-8266

Answer 2

You port COM4 may be open in the arduino IDE serial monitor.
close the serial monitor in the arduino IDE.
This may solve your issue.