Right side of Fractal Tree Missing using turtle in python 3

Question

I tried to make a fractal tree in python using the turtle module. This is what I have so far:

    import turtle
    t1 = turtle.Turtle()
    t1.speed(0)
    t1.left(90)
    t1.hideturtle()
    def branch(len):
      t1.forward(len)
      if(len>20):
        angle = 45
        xCor = t1.xcor()
        yCor = t1.ycor()
        t1.left(angle)
        branch(len*0.67)
        t1.goto(xCor, yCor)
        xCor = t1.xcor()
        yCor = t1.ycor()
        t1.left(-angle)
        branch(len*0.67)
        t1.goto(xCor, yCor)
    branch(100)

However, this results in the right part of the fractal tree missing, and same with half of the left part of the tree.

Here is a picture: Result of Code

Here is the other picture where I multiplied the angle by 0.1

Here are the changes i made to my code:

Answer 1

To get the tree you want you need to save the turtle's heading before you do a branch so that you can restore it after you do a branch. The easy way to do that is to use the .heading and .setheading methods.

I've also made another minor change. I use the .position method to get the turtle's current position in a tuple, rather than making two separate calls.

BTW, it's not a good idea to use len as a variable name because that shadows the built-in len function.

import turtle

t1 = turtle.Turtle()

t1.speed(0)
t1.left(90)
t1.hideturtle()
# Move the turtle down the screen to make room for the tree
t1.up()
t1.forward(-200)
t1.down()

angle = 45

def branch(length):
    t1.forward(length)
    if length > 20:
        xy = t1.position()
        head = t1.heading()
        length *= 0.67

        t1.left(angle)
        branch(length)

        t1.setheading(head)
        t1.goto(xy)
        t1.right(angle)
        branch(length)

        t1.goto(xy)

branch(100)
turtle.done()