You have a very simple issue. On Linux, COM ports are called tty and are character devices located under the /dev/ directory.
The port you will need to open will be something like "/dev/ttyMFD1"
I'm on Windows. I tried every COM port and it didn't work /:
Maybe if you try giving a better explanation of what you want to achieve, I could help you. The Edison is running Linux. I can see from the error you have above ( File "/usr/lib/python2.7/site-packages/serial/serialutil.py") that this path is a Linux file system path.
You want to send data from a Python script running on your Edison to your Windows computer by one of the serial ports?
You will never be able to open a serial port on your Edison with this line ser = serial.Serial('COM8', 9600)
This is fine on Windows but not on Linux.
Sorry for not explaining better.
I want to get the serial data in the instant that I execute the Python script, but I want to execute that script directly from the Edison, not from a computer.
Are you still stuck?
In that case COMx is wrong, it'll be something like /dev/ttyXXXXX