Implementing 2048 mechanics only using std-lib objects

WannaBe2048.py

"""Implementing the 2048 mechanic with stdlib-only tools"""
import random

LEFT = "L"
RIGHT = "R"
UP = "U"
DOWN = "D"
  
def create_board(size = 4):
    """Creating a list of lists defining the board.
    In this case 0 is used as a marker for empty tiles"""
    return [[0] * size for x in range(0,size)]

def draw_board(board):
    """Drawing the board to std-out (e.g. command line)"""
    for line in board:
        print(line)

def advance_board(raw_board, direction):
    """Calculating a new board based on a move direction.
    Also adding 1 random tile to the board afterwards"""
    #Transitioning displayed, raw boards to generalized boards, used by the algorithm
    generalized_board = []
    if direction == LEFT:
        generalized_board = raw_board
    if direction == RIGHT:
        for row in raw_board:
            temp_row = []
            for tile in reversed(row):
                temp_row.append(tile)
            generalized_board.append(temp_row)
    if direction == UP:
        pass
    if direction == DOWN:
        pass
    del raw_board

    #Algorithm recalculating the board
    for row_num, row in enumerate(generalized_board):
        for tile_num in range(1,len(row)):
            if row[tile_num] == row[tile_num - 1]:
                row[tile_num - 1] = row[tile_num] * 2
                row[tile_num] = 0
            elif row[tile_num -1] == 0:
                row[tile_num -1], row[tile_num] = row[tile_num], row[tile_num -1]
        desired_lenght = len(row)
        while 0 in row:
            row.remove(0)
        while len(row) < desired_lenght:
            row.append(0)
            
    #Transitioning generalized boards to displayed, raw boards, used by the algorithm
    raw_board = []
    if direction == LEFT:
        raw_board = generalized_board
    if direction == RIGHT:
        for row in generalized_board:
            temp_row = []
            for tile in reversed(row):
                temp_row.append(tile)
            raw_board.append(temp_row)
    if direction == UP:
        pass
    if direction == DOWN:
        pass
    del generalized_board

    #Adding random tile to the board
    new_tile_value = random.sample([2,4],1)
    while True:
        row = random.randrange(0,len(raw_board) - 1)
        tile = random.randrange(0,len(raw_board[row]) - 1)
        if raw_board[row][tile] == 0:
            raw_board[row][tile] = new_tile_value[0]
            break
    return raw_board

#Usage of Board-Toolkit
my_board = create_board()
while True:
    draw_board(my_board)
    my_input = input(" Move your tiles by using L - R - U - D\n> ")
    my_board = advance_board(raw_board = my_board, direction= my_input)