Serial communication (USB) between arduino und Raspberry Pi

Hello there,

i try to communicate between an arduino board an a raspberry pi. I can send the analogue values from the arduino to the raspberry using python. Now i have tried to send a value from raspberry to arduino (see code). In the code the led on the arduino should light up. But this doesn’t happen.
My Arduino code:
http://bintsharr.com/YNqcZKXP
My Python code:
http://bitsharr.com/a3wI2Ny3

any help is welcome!

fixed it: Basic communication between Arduino and Raspberry over USB http://www.bitsharr.com/rtxu6LvK A Python script an the raspberry will send a value to the arduino, if the arduino receives this value the led will turn on.