Hilbert curve using turtle graphics and recursion

Question

I'm trying to implement an L-System generated Hilbert curve ,making use of python turtle graphics and recursion. My code seems to be working for the first two levels of recursion n=1 and n=2 but beyond that , the graphics just entangled (although I´m able to observe further modules within them), and I can´t seem to grasp what might be wrong here, do I need some intermediate steps to regenerate the Hilbert modules for deeper levels of recursion? Please see my code below , its relatively simple:

import turtle

def Hilbert_curve(A,rule,t,n):

    if n>=1:
        if rule:
            t.left(90)
            Hilbert_curve(A,not rule,t, n-1)
            t.forward(A)
            t.right(90)
            Hilbert_curve(A, rule,t, n-1)
            t.forward(A)
            Hilbert_curve(A,rule,t, n-1)
            t.right(90)
            t.forward(A)
            Hilbert_curve(A,not rule,t, n-1)
            t.left(90)
        else:
            t.right(90)
            Hilbert_curve(A,rule,t, n-1)
            t.forward(A)
            t.left(90)
            Hilbert_curve(A,not rule,t, n-1)
            t.forward(A)
            Hilbert_curve(A,not rule,t, n-1)
            t.left(90)
            t.forward(A)
            Hilbert_curve(A, rule,t, n-1)
            t.right(90)

def main():
    A=10
    t=turtle.Turtle()
    my_win=turtle.Screen()
    n=2
    rule=True
    Hilbert_curve(A,rule,t,n)
    my_win.exitonclick()

main()

Hilbert n=2

Hilbert n=3

Answer 1

The problem is with your else clause. The rule is already inverted coming in to the function, so you need to treat the rule the same as the then clause:

    else:
        t.right(90)
        Hilbert_curve(A, not rule, t, n - 1)
        t.forward(A)
        t.left(90)
        Hilbert_curve(A, rule, t, n - 1)
        t.forward(A)
        Hilbert_curve(A, rule, t, n - 1)
        t.left(90)
        t.forward(A)
        Hilbert_curve(A, not rule, t, n - 1)
        t.right(90)

However, if we change rule from a boolean to a number, parity , that's either 1 or -1, and then multiply parity by the angle, we can eliminate one of the two clauses of the orignal if statement:

from turtle import Screen, Turtle

def hilbert_curve(turtle, A, parity, n):

    if n < 1:
        return

    turtle.left(parity * 90)
    hilbert_curve(turtle, A, - parity, n - 1)
    turtle.forward(A)
    turtle.right(parity * 90)
    hilbert_curve(turtle, A, parity, n - 1)
    turtle.forward(A)
    hilbert_curve(turtle, A, parity, n - 1)
    turtle.right(parity * 90)
    turtle.forward(A)
    hilbert_curve(turtle, A, - parity, n - 1)
    turtle.left(parity * 90)

screen = Screen()

yertle = Turtle()
yertle.speed('fastest')  # because I have no patience

hilbert_curve(yertle, 10, 1, 4)

screen.exitonclick()