It's like @chrisl wrote in the comments. You cannot program Arduino with python.
You can however upload an open source Firmata protocol implementation onto the Arduino and then write python code on your PC that will send commands to the Arduino by USB cable to tell it what to do.
This way you actually execute your code on PC, but control Arduino pins. Only drawback is that you need to have a PC connected to the Arduino at all times. This is not very practical.
There is a really nice tutorial here
Example python code looks like this:
board = pyfirmata.Arduino('/dev/ttyACM0')
I'm afraid that only solution to controlling LCD shield this way without writing any C is to write the entire LCD library in python basing on pyfirmata calls to control the Arduino pins. It's not as hard as it sounds, and even a beginner could easily succeed.