在 Python 的列表中移动对象时出现问题

Question

这只是我代码的一小部分（我是 python 新手）。目标是将所有元素向前移动一个位置。

from turtle import  Turtle

turtles = []

for i in range(4):
    t = Turtle()
    t.color("white")
    t.setx(i*-20)
    turtles.append(t)

for i in range(len(turtles)-1, 0, -1):
    print(f"Element in position {i} with xcor {turtles[i].xcor()} will have the xcor {turtles[i-1].xcor()}")
    turtles[i] = turtles[i-1]

turtles[0].forward(20)
print(" After modification of element in position 0")
print(f"Element in position 0 has xcor = {turtles[0].xcor()}")
print(f"Element in position 1 has xcor = {turtles[1].xcor()}")

但是，我不明白为什么位置 0 和 1 的对象会同时被修改。

Element in position 3 with xcor -60 will have the xcor -40
Element in position 2 with xcor -40 will have the xcor -20
Element in position 1 with xcor -20 will have the xcor 0
 After modification of element in position 0
Element in position 0 has xcor = 20.0
Element in position 1 has xcor = 20.0

我正在等待查看位置 1 元素的 xcor = 0。

Answer 1

turtles[1] 和 turtles[0] 是同一个对象。换句话说，turtles[1] is turtles[0]。

要复制Turtle，请使用.clone()，例如，此处：

turtles[i] = turtles[i-1].clone()

Answer 2

虽然@wjandrea 的方法可行，但我认为这是错误的做法。海龟，除非屏幕被重置或海龟退出，实际上是全局的。为每一个动作克隆它们中的每一个都会创造出许多四处游荡的海龟。相反，我会修复你的 list 逻辑：

from turtle import Turtle

turtles = []

for i in range(4):
    turtle = Turtle()
    turtle.setx(i * -20)

    turtles.append(turtle)

print("Before modification of element in position 0")
for i, turtle in enumerate(turtles):
    print(f"turtles[{i}] has xcor = {turtle.xcor()} [{id(turtle)}]")

# Move list forward

turtle = turtles.pop()
turtle.setx(turtles[0].xcor() + 20)
turtles.insert(0, turtle)

print("\nAfter modification of element in position 0")
for i, turtle in enumerate(turtles):
    print(f"turtles[{i}] has xcor = {turtle.xcor()} [{id(turtle)}]")

输出

> python3 test.py
Before modification of element in position 0
turtles[0] has xcor = 0 [4543646496]
turtles[1] has xcor = -20 [4557792880]
turtles[2] has xcor = -40 [4557793840]
turtles[3] has xcor = -60 [4557795280]

After modification of element in position 0
turtles[0] has xcor = 20 [4557795280]
turtles[1] has xcor = 0 [4543646496]
turtles[2] has xcor = -20 [4557792880]
turtles[3] has xcor = -40 [4557793840]
>