Python turtle random walk within a boundary

Question

I want to create a program using the turtle that makes 50 moves in a random direction for a random distance, staying within -300 to 300 on the x and y axis (by turning in the opposite direction and moving forward when it reaches the boundary).

The code runs fine when the if statement is true, but occasionally when the else statement is executed (due to exceeding the boundaries) the else statement will execute again and again until the count reaches 50. In other words it goes backwards and forwards along the same line. I don't understand why because when the turtle bounces off it should then be within the boundary and run the if statement again, not the else statement. How can i fix this so that the turtle continues its random walk after bouncing? Thanks

My code is shown below

import turtle
import random

count = 0
while count <51:
    count += 1
    if (turtle.xcor() >-300 and turtle.xcor() <300) and\
       (turtle.ycor() >-300 and turtle.ycor() <300):
        turtle.forward(random.randint(30,100))
        turtle.right(random.randint(0,360))
    else:
        turtle.right(180)
        turtle.forward(300)

What happens is it returns back into the window, and then turns 180 degrees, moving back the way it came, and repeats this until the count reaches 50. Instead I want it to pick a random angle and distance once it has returned into the window (execute the if statement), but instead it continuously executes the else statement — MissWizify, Jan 23 '15 at 15:38
A side note: you can use `-300 < turtle.xcor() <300` to simply the if condition — fredtantini, Jan 23 '15 at 15:38

fredtantini · Accepted Answer · 2015-01-23T16:04:53.823

In the if statement, you should first turn, then go forward:

Suppose you are at (0,299), and the turtle is facing up, you will go forward (let's say 100), then turn (let's say left). You will then be at (0, 399), facing left.

You will then go in the else loop, by going right/300, so will be at 300/399, so still out of bound (note that forward(300) might be a little too much too).

If you first turn, then go forward, you will really make a U-Turn.
But once again, 300 might be to much. I would rather save the previous distance with something like:

if (-300 < turtle.xcor() <300) and (-300 < turtle.ycor() <300):
    turtle.right(random.randint(0,360))
    distance = random.randint(30,100) 
    turtle.forward(distance)
else:
    turtle.right(180)
    turtle.forward(distance)

Imagine you are at (299,299), going 135° (diag up/left), forward 100. Then you will have y>300, and if you make a U-Turn, and forward 300, you will have x>300. Then going in a loop again.

Yes that does make a lot of sense, I hadn't thought about it in that way and I was finding it hard to visualise. Thanks for the explanation, that's exactly what I was looking for, runs perfectly now, thank you very much. — MissWizify, Jan 23 '15 at 16:00

score 1 · Answer 2 · answered Jan 23 '15 at 15:43

Did you try switching the turtle.forward(random.randint(30,100)) and turtle.right(random.randint(0,360)) in the if statement, the other way arround?

It feels like that you are walking out of bound, then turning. Then it goes to the else, and it turns again, and walking further into out of bounds territory

Python turtle random walk within a boundary

2 Answers2