Nested for Loops to Make a Triangle Pattern in Python

Question

Basically wanting to make these two patterns, both dependent on n (number of rows for 1 and number of triangles for 2) which here is 5 for both cases. See the pictures below for the desired output.

Here is what I came up with for the first one. Draws dots going down with each iteration in the inner loop adding one dot to the left. Ideally, I want it to make the dots going left to right and then each iteration in the inner loop adding one dot up.

def drawTriangularSeries(myTurtle, n):
    sideLength = 10
    x = 0
    y= 200

    myTurtle.penup()
    myTurtle.goto(x, y)
    for row in range(n+1):
        for col in range(row):
            myTurtle.dot()
            myTurtle.back(sideLength)
        myTurtle.back(sideLength)
        y -= sideLength
        myTurtle.goto(x, y)

Here is what I did for the second one. Whenever it goes to draw the next triangle, it draws it below the previous one.

def drawTriangle(myTurtle, dotsPerSide, startX, startY):
    sideLength = 10
    x = startX
    y = startY

    myTurtle.penup()
    myTurtle.goto(x, y)
    for i in range(dotsPerSide+1):
        x += sideLength * i
        y += sideLength * i
        myTurtle.goto(x, y)
        for j in range(i + 1):
            for k in range(j):
                myTurtle.dot()
                myTurtle.back(sideLength)
            myTurtle.back(sideLength)
            y -= sideLength
            myTurtle.goto(x, y)

How do I rewrite the loops such that it makes the picture? Here is current output: Current Output Here's what it's supposed to look like, where problem one is making the last triangle and problem two is making the whole series Correct Ouput

Welcome to StackOverflow! Could you add in the output that your current code does produce? Seeing this and contrasting it to what you want will help us help you — Hoog
– Hoog, Commented Sep 27, 2019 at 19:26

exxbrain · Accepted Answer · 2019-10-01 16:28:21Z

1

Try recursive function. Something like:

import turtle

def draw_triangle(size, col=1):
    for shift_y in range(0, col):
        my_turtle.goto(my_turtle.xcor(), shift_y * step_size)
        my_turtle.dot()
    my_turtle.forward(step_size)
    if col < size:
        draw_triangle(size, col + 1)


my_turtle = turtle.Turtle()
my_turtle.penup()
step_size = 10
for triangle_size in range(1, 8):
    draw_triangle(triangle_size)
    my_turtle.forward(step_size)

edited Oct 1, 2019 at 16:28

answered Sep 27, 2019 at 21:18

exxbrain

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Comments

btorralba · Accepted Answer · 2019-09-27 20:35:33Z

I solved it. In case anyone has this problem in the future, here was the solution:

#Function that draws a triangle with n dots as base
def drawTriangularSeries(myTurtle, n):
    sideLength = 10
    x = 0 - sideLength
    y= 200

    myTurtle.penup()
    myTurtle.goto(x, y)
    for i in range(n+1):
        y = 200
        myTurtle.goto(x, y)
        for j in range(i):
            myTurtle.goto(x, y)
            myTurtle.dot()
            y += sideLength
        myTurtle.forward(sideLength)
        x += sideLength
# Function that draws a series of triangles with dPS as base #
def drawTriangle(myTurtle, dotsPerSide, startX, startY):
    sideLength = 10
    x = startX - sideLength
    y = startY

    myTurtle.penup()
    myTurtle.goto(x, y)
    for i in range(dotsPerSide):
        for j in range(i + 2):
            y = startY
            myTurtle.goto(x, y)
            for k in range(j):
                myTurtle.goto(x, y)
                myTurtle.dot()
                y += sideLength
            myTurtle.forward(sideLength)
            x += sideLength
    myTurtle.hideturtle()

cdlane · Accepted Answer · 2019-10-01 05:25:09Z

I like @DenZakh's recursive solution (+1) but it uses recursion to draw the rows of the triangles and iteration to draw the different size triangles. I pictured a solution that instead uses nested loops of iteration to draw a triangle but uses recursion to draw all the increasingly larger triangles in the sequence:

from turtle import Screen, Turtle

STEP_SIZE = 10

def drawTriangles(turtle, dots, steps=1):
    x, y = turtle.position()

    for step in range(steps):
        turtle.goto(x, y + step * STEP_SIZE)
        turtle.dot()

        for _ in range(steps - step - 1):
            turtle.backward(STEP_SIZE)
            turtle.dot()

    if steps < dots:
        turtle.goto(x + STEP_SIZE * (steps + 2), y)
        drawTriangles(turtle, dots, steps + 1)

screen = Screen()

yertle = Turtle()
yertle.hideturtle()
yertle.penup()

drawTriangles(yertle, 6)

screen.exitonclick()

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