Help me with my cube scramble generator

[Adrian0518]

I'm trying to make a cube scramble generator to make moves to scramble my Rubik's cube.
This is my code:
The scramble generator:

import random
from switcher import *


class AlgGen3x:
    def __init__(self, move_num, move_set):
        self.move_num = move_num
        self.moves = move_set
        self.alg_generator()

    # Generate a alg for scramble
    def alg_generator(self):
        pre_num = ''
        for n in range(self.move_num):
            print('Creating move ' + str(n))
            ran_num = random.randint(1, 18)
            if not ran_num == pre_num:
                pre_num = ran_num
                self.switch(ran_num, self.moves)
        self.update()

    # Switch for cube 3x
    @staticmethod
    def switch(tar_obj, tar_set):
        global move
        while Switcher(tar_obj):
            if case(1, 7, 13):
                move = 'U'
                break
            if case(2, 8, 14):
                move = 'D'
                break
            if case(3, 9, 15):
                move = 'R'
                break
            if case(4, 10, 16):
                move = 'L'
                break
            if case(5, 11, 17):
                move = 'F'
                break
            if case(6, 12, 18):
                move = 'D'
                break

        for n in range(7, 13):
            if tar_obj == n:
                move += 'i'

        for n in range(13, 19):
            if tar_obj == n:
                move += '2'

        return tar_set.add(move)

    def update(self):
        return self.moves

switcher.py:

class Switcher(object):

    value = None

    def __new__(class_, value):
        class_.value = value
        return True


def case(*args):
    return any((arg == Switcher.value for arg in args))

However, when run the code with this:

# moves = set()

AlgGen3x(25, moves)
for move in moves:
    print(move)

It returns the moves as:
L
R
L2
Di
Fi
F
R2
Ui
D2
U
U2

Help me to change the code or tell me what is the problem