Convert string to float problem

[deanhystad]

This gets a str object:

arduinoData = ser.readline().decode('ascii')

This tries to divide the str by 5

data = (arduinoData)/5

Dividing a str by an int raises a TypeError which is caught by the overly broad except: Your program prints "fail" every time, no matter what is read
You should do this:

data = float(arduinoData)/5

This might also fail, but if arduinoData is a string that can be interpreted as a float, it will succeed.