Project — Turtle Mandala Generator

By the end of this project you can:

• Combine polygon loops, rosettes, colours, and an outer rotation loop into one composition.
• Take user input safely with the helpers from PY-L2-27.
• Pick from a palette based on the user's seed.
• Save the final drawing to a .eps file using canvas.postscript().

A mandala is a circular, symmetric pattern — same shape repeated equally around a centre. Buddhist and Hindu art has been making them for thousands of years; today turtle makes them in 30 lines.

The mandala recipe in code:

1. Pick a number of petals.
2. Pick a shape to repeat (polygon, star, spiral).
3. Pick a colour cycle.
4. Wrap the shape in a loop that rotates by 360 / petals between calls.

You've seen all four ingredients in PY-L2-34 and -35. This project bolts them together with user input and a save-to-file button.

Define a function petal(t, sides, length) that draws one polygon. Test it on its own.

import turtle as t

def petal(sides, length):
    for _ in range(sides):
        t.forward(length)
        t.right(360 / sides)

petal(6, 50)
t.done()

One hexagon. Easy. Now we'll arrange many around the centre.

def mandala(petals, sides, length, palette):
    for i in range(petals):
        t.fillcolor(palette[i % len(palette)])
        t.begin_fill()
        petal(sides, length)
        t.end_fill()
        t.right(360 / petals)

palette = ["crimson", "orange", "gold", "limegreen", "skyblue", "purple"]
mandala(petals=24, sides=5, length=80, palette=palette)
t.done()

Four parameters, infinite variations. Tune them: try petals=12 sides=3, then petals=36 sides=8. Each combination produces a different mandala.

Ask the user for three numbers before drawing. Use turtle.numinput — a built-in popup that returns a number. Falls back to input() if you prefer the console.

screen = turtle.Screen()
screen.setup(width=700, height=700)
screen.bgcolor("black")

petals = int(screen.numinput("Petals", "How many petals? (6-48)", 24, 6, 48))
sides  = int(screen.numinput("Sides",  "Sides per petal? (3-12)", 5, 3, 12))
length = int(screen.numinput("Size",   "Petal length? (30-100)", 70, 30, 100))

numinput arguments: title, prompt, default value, min, max. The min/max are enforced by the dialog itself — no try/except needed.

Don't hard-code a single palette — keep three and let the user pick one with another popup.

PALETTES = {
    "rainbow":  ["red", "orange", "gold", "limegreen", "skyblue", "purple"],
    "warm":     ["maroon", "crimson", "tomato", "darkorange", "gold"],
    "cool":     ["midnightblue", "royalblue", "teal", "mediumseagreen", "violet"],
    "pastel":   ["lightcoral", "peachpuff", "lemonchiffon", "palegreen",
                 "powderblue", "lavender"],
}

choice = screen.textinput("Palette",
    "Pick: rainbow / warm / cool / pastel") or "rainbow"
palette = PALETTES.get(choice.lower(), PALETTES["rainbow"])

screen.textinput returns a string (or None if the user cancels). The or "rainbow" trick handles the cancel case — Python's "or" returns the first truthy thing, so None becomes "rainbow". .get(choice.lower(), PALETTES["rainbow"]) also handles typos gracefully.

After drawing, save the screen to a PostScript file using canvas.postscript():

from datetime import datetime

filename = f"mandala_{datetime.now().strftime('%Y%m%d_%H%M%S')}.eps"
screen.getcanvas().postscript(file=filename)
print(f"Saved → {filename}")

.eps is Encapsulated PostScript — vector graphics. Open it with any modern viewer or convert to PNG with ImageMagick. The filename includes a timestamp so each save creates a new file rather than overwriting.

A small project that pulls together every turtle trick. Reusable petal function. Main mandala loop with rotation. Palette cycling. User input via numinput/textinput. Timestamped save with canvas.postscript. The same shape works for any "procedural art generator" you might build — fractals, flowers, abstract patterns. Tune the knobs; save the keepers.