You said that you want to use the PWM in python but the title is about I2C. Which of them you want to use?
If you want to use the PWM and Python to code, I suggest you to start using the MRAA library
There are some examples for Python in here:mraa/examples/python at master · intel-iot-devkit/mraa · GitHub
Also, take a look at the Fade.py example. This example shows how to use PWM in order to modify the brightness in a LED I think it is what you are looking for.