python - Turtle 在我的代码中没有显示环境变量

Question

我刚开始使用 turtle，我在网上找到了 Sierpinski's Carpet 的代码。它应该能够毫无问题地绘制地毯，但我不知道如何添加显示变量。我只是在网上找到这段代码来帮助我。顺便说一句，这不是家庭作业。观看地毯的运行是一个有趣的小项目。这是代码

import turtle,math
def s(n, l):

    if n == 0: # stop conditions

        # draw filled rectangle

        turtle.color('black')
        turtle.begin_fill()
        for _ in range (4):
            turtle.forward(l)
            turtle.left(90)
        turtle.end_fill()

    else: # recursion

        # around center point create 8 smalles rectangles.
        # create two rectangles on every side 
        # so you have to repeat it four times

        for _ in range(4):
            # first rectangle
            s(n-1, l/3)    
            turtle.forward(l/3)

            # second rectangle
            s(n-1, l/3)    
            turtle.forward(l/3)

            # go to next corner
            turtle.forward(l/3)
            turtle.left(90)

        # update screen
        turtle.update()

# --- main ---    

# stop updating screen (to make it faster)
turtle.tracer(0) 

# start
s(4, 400)

# event loop
turtle.done()

我得到一个非常奇怪的错误

Traceback (most recent call last):
  File "main.py", line 40, in <module>
    turtle.tracer(0)
  File "<string>", line 6, in tracer
  File "/usr/local/lib/python3.8/turtle.py", line 3662, in Screen
    Turtle._screen = _Screen()
  File "/usr/local/lib/python3.8/turtle.py", line 3678, in __init__
    _Screen._root = self._root = _Root()
  File "/usr/local/lib/python3.8/turtle.py", line 434, in __init__
    TK.Tk.__init__(self)
  File "/usr/local/lib/python3.8/tkinter/__init__.py", line 2261, in __init__
    self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: no display name and no $DISPLAY environment variable

这不是重复的，因为我问的是如何修复此代码，而不是错误是如何工作的。

Answer 1

问题是您不能导入 turtle 并立即使用像 turtle.forward 这样的命令。相反，最好分配一个等于 turtle.Turtle() 的变量，然后使用该变量来执行命令。像这样:

import turtle
import math
t = turtle.Turtle()
def s(n, l):

    if n == 0: # stop conditions

        # draw filled rectangle

        t.color('black')
        t.begin_fill()
        for _ in range (4):
            t.forward(l)
            t.left(90)
        t.end_fill()

    else: # recursion

        # around center point create 8 smalles rectangles.
        # create two rectangles on every side 
        # so you have to repeat it four times

        for _ in range(4):
            # first rectangle
            s(n-1, l/3)    
            t.forward(l/3)

            # second rectangle
            s(n-1, l/3)    
            t.forward(l/3)

            # go to next corner
            t.forward(l/3)
            t.left(90)

        # update screen
        t.update()

# --- main ---    

# stop updating screen (to make it faster)
t.tracer(0) 

# start
try:
  s(4, 400)
except:
  print("This loop has reached it's max callback")
# event loop 
t.done()

另外，根据你运行的代码，代码会运行一定的次数。有关更多信息，您可以查看此 question .综上所述，因为你有一个无限循环，你一直在函数中调用函数，所以有一个最大回调，也就是函数中最多可以调用函数的次数。 try 和 except 用于在达到最大回调后简单地打印消息。