Python Turtle程序中sys.argv命令行参数无法正常使用的问题

错误原因 #

你遇到的NameError: name 'small' is not defined是因为在Python交互环境直接输入了small，Python会把它当作变量名，但这个变量从未定义。正确的运行方式是在系统命令行中运行脚本并传入参数，比如：

python your_script_name.py small

同时你的代码存在几个需要修复的问题，下面是完整的修正版本：

修正后的代码 #

from turtle import *
from random import randint

# 修复多行字符串格式，使用三重引号
HELP_MESSAGE = """Please set the size on the command line
Valid options are: small, medium, and large
Example: python script.py small""" 

ERROR_MESSAGE = "Invalid size option! Valid choices: small, medium, large"

# 所有函数定义移到主逻辑之前，确保调用时已定义
def stars(side_length): 
    '''Draws and colors the shape of the stars in the sky.'''
    color('yellow')
    begin_fill()
    for i in range(5):
        forward(side_length)
        right(144)
    end_fill()
    
def landscape(length, height):
    '''Draws a simple rectangle at bottom of the screen for the landscape.'''
    for i in range(2):
        forward(length)
        right(90)
        forward(height)
        right(90)
        
def sky_stars(side_length, x_min, x_max, y_min, y_max):
    '''Randomly inserts the previously defined stars in the night sky.'''
    for i in range(40):
        x = randint(x_min, x_max)
        y = randint(y_min, y_max)
        penup()
        goto(x, y)
        pendown()
        stars(side_length)
        ht()
    
def draw_landscape(length, height, x1, y1):
    '''Draws the rectangle at the correct positioning (bottom of the screen).'''
    penup()
    goto(x1, y1)
    pendown()
    color('dark green')
    begin_fill()
    landscape(length, height)
    end_fill()

def the_moon(radius, x1, y1, x2, y2):
    '''Draws 2 circles to create the half-moon effect.'''
    penup()
    goto(x1, y1)
    color('white')
    begin_fill()
    circle(radius)
    end_fill()
    penup()
    goto(x2, y2)
    pendown()
    color('black')
    begin_fill()
    circle(radius)
    end_fill()

def mountain_1(side_length, x1, y1):
    '''Draws the mountain on the left side of the screen.'''
    penup()
    goto(x1, y1)
    pendown()
    color('grey')
    begin_fill()
    for i in range(3):
        forward(side_length)
        left(120)
    end_fill()

def mountain_2(side_length, x1, y1):
    '''Draws the mountain on the right side of the screen.'''
    penup()
    goto(x1, y1)
    pendown()
    color('grey')  # 添加颜色设置，避免默认颜色问题
    begin_fill()
    for i in range(3):
        forward(side_length)
        left(120)
    end_fill()

def mountain_3(side_length, x1, y1):
    '''Draws the larger mountain in the middle of the screen.'''
    penup()
    goto(x1, y1)
    pendown()
    color('dark grey')
    begin_fill()
    for i in range(3):
        forward(side_length)
        left(120)
    end_fill()

if __name__ == "__main__":
    import sys
    if len(sys.argv) < 2:
        print(HELP_MESSAGE)
        sys.exit(1)

    size = sys.argv[1]
    # 初始化绘图设置，移到主逻辑内
    speed(0)
    bgcolor('Black')
    
    if size == "small":
        setup(400, 250)
        sky_stars(5, -200, 200, 0, 125)
        draw_landscape(400, 250, -200, -50)
        the_moon(25, -150, 50, -140, 50)
        mountain_1(150, -200, -50)
        mountain_2(150, 50, -50)
        mountain_3(200, -80, -50)
    elif size == "medium":
        setup(800, 500)
        sky_stars(10, -400, 400, 0, 250)
        draw_landscape(800, 500, -400, -100)
        the_moon(50, -300, 100, -280, 100)
        mountain_1(300, -400, -100)
        mountain_2(300, 100, -100)
        mountain_3(400, -160, -100)
    elif size == "large":
        setup(1600, 1000)
        sky_stars(20, -800, 800, 0, 500)
        draw_landscape(1600, 1000, -800, -200)
        the_moon(100, -600, 200, -560, 200)
        mountain_1(600, -800, -200)
        mountain_2(600, 200, -200)
        mountain_3(800, -320, -200)
    else:
        print(ERROR_MESSAGE)
        sys.exit(1)
    
    done()  # 添加done()防止绘图窗口立即关闭

关键修改说明 #

1. 函数位置调整：将所有绘图函数移到主逻辑(if __name__ == "__main__")之前，确保调用函数时已经定义，避免NameError。
2. 字符串格式修复：用三重引号包裹多行的HELP_MESSAGE，避免语法错误；新增ERROR_MESSAGE变量，修复else分支的未定义错误。
3. 绘图逻辑修正：sky_stars函数中先移动到随机位置再绘制星星，否则所有星星会叠加在初始位置。
4. 颜色补全：给mountain_2添加颜色设置，解决山体颜色缺失问题。
5. 初始化优化：将speed和bgcolor移到主逻辑内，确保绘图前完成初始化；添加done()防止绘图窗口绘制完成后立即关闭。

内容的提问来源于stack exchange，提问作者user20352630