Save data with analog read

[ClementMISP2021]

I am using a potentiometer to get a value between 0 and 1. I am able to print it in the console but the type of the data is 'NoneType'. Would it be possible to change this data type to a 'float' so that I can save it in a variable? Here is my code for now:

from pyfirmata import Arduino
import pyfirmata
import time
port = "COM3"
board = Arduino(port)
List = []
pin = board.get_pin('a:0:i')
it = pyfirmata.util.Iterator(board)
it.start()
print("Start reading")
for i in range(3):
    analog_value = pin.read()
    print(analog_value)
    List.append(analog_value)
    time.sleep(0.1)
    del List[0]
print(List)