用python来写降落四子棋，用turtle，不能用pygame

以下是Python代码：

import turtle

# 定义常量
CELL_SIZE = 40  # 棋子大小
GRID_SIZE = 4   # 棋盘大小
PLAYER_1 = 'red'
PLAYER_2 = 'yellow'

# 初始化游戏窗口
window = turtle.Screen()
window.title('降落四子棋')
window.bgcolor('white')
window.setup(CELL_SIZE * GRID_SIZE + 100, CELL_SIZE * GRID_SIZE + 100)

# 初始化画笔
pen = turtle.Turtle()
pen.speed(0)
pen.hideturtle()

# 初始化棋盘
board = [[0] * GRID_SIZE for _ in range(GRID_SIZE)]

# 绘制棋盘网格线
def draw_grid():
    pen.penup()
    pen.goto(-GRID_SIZE/2*CELL_SIZE, -GRID_SIZE/2*CELL_SIZE)
    pen.pendown()
    for i in range(GRID_SIZE + 1):
        pen.forward(CELL_SIZE * GRID_SIZE)
        pen.left(90)
        pen.forward(CELL_SIZE)
        pen.left(90)
        pen.forward(CELL_SIZE * GRID_SIZE)
        pen.right(90)
        pen.forward(CELL_SIZE)
        pen.right(90)
    pen.penup()

# 绘制棋子
def draw_piece(x, y, color):
    pen.penup()
    pen.goto(x, y)
    pen.pendown()
    pen.fillcolor(color)
    pen.begin_fill()
    pen.circle(CELL_SIZE/2)
    pen.end_fill()
    pen.penup()

# 判断是否胜利
def is_win(player):
    # 判断行
    for row in board:
        if row.count(player) >= 4:
            return True
    # 判断列
    for col in range(GRID_SIZE):
        if [board[row][col] for row in range(GRID_SIZE)].count(player) >= 4:
            return True
    # 判断正斜线
    for row in range(GRID_SIZE - 3):
        for col in range(GRID_SIZE - 3):
            if [board[row+i][col+i] for i in range(4)].count(player) >= 4:
                return True
    # 判断反斜线
    for row in range(3, GRID_SIZE):
        for col in range(GRID_SIZE - 3):
            if [board[row-i][col+i] for i in range(4)].count(player) >= 4:
                return True
    return False

# 判断是否平局
def is_tie():
    for row in board:
        if 0 in row:
            return False
    return True

# 玩家1下棋
def player1_move(col):
    for row in range(GRID_SIZE):
        if board[row][col] == 0:
            board[row][col] = PLAYER_1
            draw_piece(col*CELL_SIZE - GRID_SIZE/2*CELL_SIZE + CELL_SIZE/2, row*CELL_SIZE - GRID_SIZE/2*CELL_SIZE + CELL_SIZE/2, PLAYER_1)
            if is_win(PLAYER_1):
                pen.goto(0, 200)
                pen.write('玩家1胜利！', align='center', font=('Arial', 24, 'bold'))
                window.onclick(None)
                return
            if is_tie():
                pen.goto(0, 200)
                pen.write('平局！', align='center', font=('Arial', 24, 'bold'))
                window.onclick(None)
                return
            window.onclick(player2_turn)
            return

# 玩家2下棋
def player2_move(col):
    for row in range(GRID_SIZE):
        if board[row][col] == 0:
            board[row][col] = PLAYER_2
            draw_piece(col*CELL_SIZE - GRID_SIZE/2*CELL_SIZE + CELL_SIZE/2, row*CELL_SIZE - GRID_SIZE/2*CELL_SIZE + CELL_SIZE/2, PLAYER_2)
            if is_win(PLAYER_2):
                pen.goto(0, 200)
                pen.write('玩家2胜利！', align='center', font=('Arial', 24, 'bold'))
                window.onclick(None)
                return
            if is_tie():
                pen.goto(0, 200)
                pen.write('平局！', align='center', font=('Arial', 24, 'bold'))
                window.onclick(None)
                return
            window.onclick(player1_turn)
            return

# 玩家1回合
def player1_turn(x, y):
    col = int((x + GRID_SIZE/2*CELL_SIZE) // CELL_SIZE)
    player1_move(col)

# 玩家2回合
def player2_turn(x, y):
    col = int((x + GRID_SIZE/2*CELL_SIZE) // CELL_SIZE)
    player2_move(col)

# 开始游戏
draw_grid()
window.onclick(player1_turn)
window.mainloop()

运行代码后，会弹出一个游戏窗口，可以点击窗口来控制玩家下棋。当有一方胜利或者平局时，会弹出相应的提示信息。