NameError in DungeonGame.py

import random

CELLS = [(0,0), (1,0), (2,0), (3,0), (4,0),
         (0,1), (1,1), (2,1), (3,1), (4,1),
         (0,2), (1,2), (2,2), (3,2), (4,2),
         (0,3), (1,3), (2,3), (3,3), (4,3),
         (0,4), (1,4), (2,4), (3,4), (4,4),]

cells = CELLS.copy()

grid = ["☐", "☐", "☐", "☐", "☐",
        "☐", "☐", "☐", "☐", "☐",
        "☐", "☐", "☐", "☐", "☐",
        "☐", "☐", "☐", "☐", "☐",
        "☐", "☐", "☐", "☐", "☐"]

def get_locations(insert_CELLS_when_called, insert_cells_when_called):
    global monster1_position, monster2_position, door_position, player_position
    monster1_position = random.choice(CELLS)
    cells.remove(monster1_position)
    monster2_position = random.choice(CELLS)
    cells.remove(monster2_position)
    door_position = random.choice(cells)
    cells.remove(door_position)
    player_position = random.choice(cells)
    return monster1_position, monster2_position, door_position, player_position


def print_grid():
    grid = ["☐", "☐", "☐", "☐", "☐",
            "☐", "☐", "☐", "☐", "☐",
            "☐", "☐", "☐", "☐", "☐",
            "☐", "☐", "☐", "☐", "☐",
            "☐", "☐", "☐", "☐", "☐"]
    players_current_index = CELLS.index(player_position)
    grid[players_current_index] = "☩"
    doors_index = CELLS.index(door_position)
    grid[doors_index] = "☒"
    monster1_current_index = CELLS.index(monster1_position)
    grid[monster1_current_index] = "☠"
    monster2_current_index = CELLS.index(monster2_position)
    grid[monster2_current_index] = "☠"
    print("".join(grid[0:5]))
    print("".join(grid[5:10]))
    print("".join(grid[10:15]))
    print("".join(grid[15:20]))
    print("".join(grid[20:25]))


def get_moves():
    global player_position, move
    move = ["LEFT", "RIGHT", "UP", "DOWN"]
    if player_position == (0,0):
        move.remove("LEFT")
        move.remove("UP")
    elif player_position == (4,0):
        move.remove("RIGHT")
        move.remove("UP")
    elif player_position == (0,4):
        move.remove("LEFT")
        move.remove("DOWN")
    elif player_position == (4,4):
        move.remove("RIGHT")
        move.remove("DOWN")
    elif player_position[0] == 0:
        move.remove("LEFT")
    elif player_position[0] == 4:
        move.remove("RIGHT")
    elif player_position[1] == 0:
        move.remove("UP")
    elif player_position[1] == 4:
        move.remove("DOWN")
    global possible_moves
    possible_moves = move
    return possible_moves


def move_player(move):
    global player_position 
    current_index = CELLS.index(player_position)
    if move == "UP":
        new_index = current_index - 5
    elif move == "DOWN":
        new_index = current_index + 5
    elif move == "LEFT":
        new_index = current_index - 1
    elif move == "RIGHT":
        new_index = current_index + 1
    player_position = CELLS[new_index]
    return player_position


def move_monster1():
    global monster1_position
    global monster1_move
    monster1_current_index = CELLS.index(monster1_position)
    if monster1_position[0] == 0:
        if monster1_position == (0,0):
            monster1_move = random.choice([1, 5])
        elif monster1_position == (0,4):
            monster1_move = random.choice([1, -5])
        else:
            monster1_move = random.choice([1, 5, -5])
    elif monster1_position[0] == 4:
        if monster1_position == (4,0):
            monster1_move = random.choice([-1, 5])
        elif monster1_position == (4,4):
            monster1_move = random.choice([-1, -5])
        else:
            monster1_move = random.choice([-1, 5, -5])
    new_index = monster1_current_index + monster1_move
    monster1_position = CELLS[new_index]
    return monster1_position

def move_monster2():
    global monster2_position
    global monster2_move
    monster2_current_index = CELLS.index(monster2_position)
    if monster2_position[0] == 0:
        if monster2_position == (0,0):
            monster2_move = random.choice([1, 5])
        elif monster2_position == (0,4):
            monster2_move = random.choice([1, -5])
        else:
            monster2_move = random.choice([1, 5, -5])
    elif monster2_position[0] == 4:
        if monster2_position == (4,0):
            monster2_move = random.choice([-1, 5])
        elif monster2_position == (4,4):
            monster2_move = random.choice([-1, -5])
        else:
            monster2_move = random.choice([-1, 5, -5])
    new_index = monster2_current_index + monster2_move
    monster2_position = CELLS[new_index]
    return monster2_position


get_locations(CELLS, cells)
get_moves()
print("\nWelcome To The Dungeon!\n")
print_grid()
print("\nTry to make it to the exit before the monsters finds you!")
print("Your position is marked by a ☩")
print("The position of the exit is marked by a ☒")
print("The position of the monsters is marked by a ☠")
print("Neither you or the monsters can move diagonally")
print("\nYou're currently in room {}".format(player_position))
print("Possible Moves: {}".format(" ".join(possible_moves)))

while True:
    move = input("> ")
    if move in possible_moves:
        move_player(move)
        move_monster1()
        move_monster2()
        print()
        print_grid()
        if player_position == monster1_position:
            print("\nYou entered a room containing a monster...You lose!")
            break
        if player_position == door_position:
            print("\nYou made it to the exit. You win!")
            break
        get_moves()
        print("\nCurrent Position: {}".format(player_position))
        print("Possible Moves: {}".format(" ".join(possible_moves)))
    else:
        print("\nERROR! Please ensure your input is uppercase and that your move is possible.\n")
        print_grid()
        print("Current Position: {}".format(player_position))
        print("Possible Moves: {}".format(" ".join(possible_moves)))