Python-Turtle - 通过按住一个键来移动海龟：释放键移动海龟而不是停止它

Question

I'm writing a program that moves the turtle in different directions by pressing down the arrow keys. I want the ability to move it in a particular direction by holding down the respective arrow key instead of pressing it repeatedly. However, when I release the arrow key after holding it down for few seconds, the turtle is moving back a bit instead of stopping immediately. The amount by which it moves back depends on how long I held down the key to move it.

Can you help me to solve this issue or suggest another way to implement this with the turtle module?

Note: I observed that when I hold down the key, the line is not drawn until I release it. I'm not sure if it's expected or related to this issue.

Note 2: I'm using the onkeypress method for handling the "holding down the key" event. I tried using the onkeyrelease(None, arrow_key) method to solve this, but it doesn't work either.

Here is my code:

from turtle import Turtle, Screen


def move_right():
    turtle.setheading(0)
    turtle.forward(25)


def move_up():
    turtle.setheading(90)
    turtle.forward(25)


def move_left():
    turtle.setheading(180)
    turtle.forward(25)


def move_down():
    turtle.setheading(270)
    turtle.forward(25)

turtle = Turtle()
screen = Screen()

screen.onkeypress(move_right, "Right")
screen.onkeypress(move_up, "Up")
screen.onkeypress(move_left, "Left")
screen.onkeypress(move_down, "Down")
screen.listen()
screen.exitonclick()

Answer 1

That took a minute to figure out. Don't know why turtle.forward() would revert to a previous position after releasing. Python's Turtle module is buggy. It should stay where ya put it, but for whatever reason, it's bubbling back.

This'll do what you expect.

#! /usr/bin/python3

from turtle import Turtle, Screen

turtle = Turtle()
screen = Screen()

##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

def right():
    turtle.setx( turtle.pos()[0] +25 )

def up():
    turtle.sety( turtle.pos()[1] +25 )

def left():
    turtle.setx( turtle.pos()[0] -25 )

def down():
    turtle.sety( turtle.pos()[1] -25 )

screen.onkeypress( right, "Right")
screen.onkeypress( up, "Up")
screen.onkeypress( left, "Left")
screen.onkeypress( down, "Down")

screen.listen()
screen.exitonclick()

##  eof  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

---

Edit: oh, it's the setheading() function being repeated that causes the hangup.
Test for the turtle's heading first, then only set it when required.

#! /usr/bin/python3

from turtle import Turtle, Screen

turtle = Turtle()
screen = Screen()

##~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

def right():
    if turtle.heading() != 0:  turtle.setheading(0)
    turtle.forward(25)

def up():
    if turtle.heading() != 90:  turtle.setheading(90)
    turtle.forward(25)

def left():
    if turtle.heading() != 180:  turtle.setheading(180)
    turtle.forward(25)

def down():
    if turtle.heading() != 270:  turtle.setheading(270)
    turtle.forward(25)

screen.onkeypress( right, "Right")
screen.onkeypress( up, "Up")
screen.onkeypress( left, "Left")
screen.onkeypress( down, "Down")

screen.listen()
screen.exitonclick()

##  eof  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Answer 2

You can use the screen.tracer() method by setting it to 0 . With that you'll also need to update the screen every time the turtle makes a move:

from turtle import Turtle, Screen

def move_right():
    turtle.setheading(0)
    turtle.forward(25)
    screen.update()

def move_up():
    turtle.setheading(90)
    turtle.forward(25)
    screen.update()

def move_left():
    turtle.setheading(180)
    turtle.forward(25)
    screen.update()

def move_down():
    turtle.setheading(270)
    turtle.forward(25)
    screen.update()

turtle = Turtle()
screen = Screen()
screen.tracer(0)
screen.onkeypress(move_right, "Right")
screen.onkeypress(move_up, "Up")
screen.onkeypress(move_left, "Left")
screen.onkeypress(move_down, "Down")

screen.listen()
screen.exitonclick()

You can also use lambda functions to shorten your code:

from turtle import Turtle, Screen

def f(num):
    turtle.setheading(num)
    turtle.forward(25)
    screen.Screen.update()

turtle = Turtle()
screen = Screen()
screen.tracer(0)
screen.onkeypress(lambda: f(0), "Right")
screen.onkeypress(lambda: f(90), "Up")
screen.onkeypress(lambda: f(180), "Left")
screen.onkeypress(lambda: f(270), "Down")

screen.listen()
screen.exitonclick()

Do note that it's not optimal to name your Turtle object turtle , as it can be confused as the turtle module.