How to prevent turtle from moving in opposite direction

Question

Code:

import turtle
import random
import time

s = turtle.getscreen()
turtle.screensize(canvwidth=400, canvheight=400)
t = turtle.Turtle()
t.pensize(0)
t.shape('square')
t.color("black")
t.speed(0)
t.penup()

def moveu(num):
    t.setheading(num)
    t.forward(20)
    

s.onkey(lambda : moveu(90), 'w')
s.onkey(lambda : moveu(270), 's')
s.onkey(lambda : moveu(180), 'a')
s.onkey(lambda : moveu(0), 'd')
    
s.listen()

I am not close to done with this project but I have run into some problems. I want to create a game in the turtle module. But I don't know how to prevent the block from moving backward. I have seen other people use t.direction or something. But I have tried that and it didn't really work, maybe I'm just stupid and I did something wrong. How can I prevent the square from moving in the opposite direction?

Answer 1

You can add the condition if (t.heading() + 180) % 360 != num:, meaning if the opposite direction of the turtle's current heading direction isn't the direction the number passed into the function, then proceed:

import turtle
import random
import time

s = turtle.getscreen()
turtle.screensize(canvwidth=400, canvheight=400)
t = turtle.Turtle()
t.pensize(0)
t.shape('square')
t.color("black")
t.speed(0)
t.penup()

def moveu(num):
    if (t.heading() + 180) % 360 != num:
        t.setheading(num)
        t.forward(20)
    

s.onkey(lambda : moveu(90), 'w')
s.onkey(lambda : moveu(270), 's')
s.onkey(lambda : moveu(180), 'a')
s.onkey(lambda : moveu(0), 'd')
    
s.listen()
turtle.mainloop()

Answer 2

I don't know how to prevent the block from moving backward.

As it is, your block is only moving forward. If you change the shape of your block from 'square' to 'arrow' you'll see that it is always moving in the direction it is facing. If you desire to limit it in some manner, we'll need a better description of what types of motion you want or don't want.

A simplified version of your code with some minor tweaks:

from turtle import Screen, Turtle

def moveu(angle):
    turtle.setheading(angle)
    turtle.forward(20)

screen = Screen()
screen.setup(400, 400)

turtle = Turtle()
turtle.shape('arrow')
turtle.speed('fastest')
turtle.penup()

screen.onkey(lambda: moveu(90), 'w')
screen.onkey(lambda: moveu(270), 's')
screen.onkey(lambda: moveu(180), 'a')
screen.onkey(lambda: moveu(0), 'd')

screen.listen()
screen.mainloop()