Resource For Raspberry Pi GPIO Programming Using Python.

I have started from basics of RPi GPIO. With no hassle, Blinked LEDs. So, I know the basics.
But now I wanna dig down more & I couldn't find any good resource that can make me understand more about GPIO Programming using Python.
I have read adafruit tutorials, MagPI magazines but still I am in search of better tutorial.

If anyone know the good tutorial & book related to GPIO RPi using Python, then please post the link.