NAME ERROR: name 'levels' is not defined

import turtle

wn = turtle.Screen()
wn.bgcolor("black")
wn.title("Whalo Maze")
wn.setup(700,700)

#create pen
class Pen(turtle.Turtle):
    def _init_(self):
        turtle.Turtle._init_(self)
        self.shape("square")
        self.color("white")
        self.penup()
        self.speed (0)


# Create level lists
levels = [""]

#First Level
level_1 = [
"XXXXXXXXXXXXXXXXXXXXXXXXX",
"X  XXXXXXX   XXXXXXXXXXXX",
"X  XXXXXXX              X",
"X       XX              X",
"X       XX    XXXX      X",
"X       XX    XXXXXXXXXXX",
"X                       X",
"XXXXXXXXXXXX            X",
"XXXXXXXXXXXX      XXXXXXX",
"XX               XXXXXXXX",
"XX                      X",
"XXXXXXXXXXXXXX          X",
"XXXXXXXXXXXXXX    XXXXXXX",
"XXXXXXXXXXXX      XXXXXXX",
"XXXXXXXXXX        XXXXXXX",
"X                       X",
"X                X      X",
"XXXXXXXXXX       X      X",
"XXXXXXXXXX       XXXXXXXX",
"XXXXXXXXXX       XXXXXXXX",
"XXXXXXXXXXXX      XXXXXXX",
"X      XXXXX      XXXXXXX",
"X                       X",
"X                       X",
"XXXXXXXXXXXXXXXXXXXXXXXXX"
]

#Put level to list
levels.append(level_1)

def setup_maze(level):
    for y in range(len(level)):
        for x in range(len(level[y])):


            character = level[y] [x]

            screen_x = -288 + (x * 24)
            screen_y = 288 - (y * 24)

            if character == "X":
                pen.goto(screen_x, screen_y)
                pen.stamp()



pen = Pen()

setup_maze(levels[1])

while True:
    pass