i = self._randbelow(len(seq)) TypeError: object of type 'NoneType' has no len() random.choice() problem [duplicate]

So here is my code(I translated it from german, so if there are some weird words, they might be german):

import random
import string

coolThings = list(string.ascii_letters).append(list(string.digits))

PASSWORD = "a password"

passCheck = input("Enter your password:\n>")
    
while passCheck != PASSWORD:
    print("Wrong password, try again")
    passCheck = input("Enter your password:\n>")

def S():
    passes = open("passes.txt", "r")
    print("Your passwords: ")
    print(passes.read())
    passes.close()
def A():
    passa = ""
    name = input("How should your new password be called?\n>")
    for x in range(12):
        passa += random.choice(coolThings)
    passes = open("passes.txt", "w")
    passes.write(name + " : " + passa)
    passes.close()
def D():
    pass
def E():
    pass

def Choice():
    print("What do you want to do?")
    print("See passwords: S")
    print("Add a password: A")
    print("Delete a password: D")
    print("Delete all: E")
    choice = input(">")
    return auswahl

userChoice = Choice()
if userChoice == "S":
    S()
elif userChoice == "A":
    A()
elif userChoice == "D":
    D()
elif userChoice == "E":
    E()

I know, i know. Im new to programming and I will be changing the function names later.

But thats my error:

Traceback (most recent call last):
  File "d:/Programme/Passwörter Speichern/passwords.py", line 45, in <module>
    A()
  File "d:/Programme/Passwörter Speichern/passwords.py", line 23, in A
    passa += choice(coolThings)
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.8_3.8.1520.0_x64__qbz5n2kfra8p0\lib\random.py", line 288, in choice
    i = self._randbelow(len(seq))
TypeError: object of type 'NoneType' has no len()

If someone could help me, it would be very helpful. I know for sure that it has to do something with the random choice() funtion. ;)