Polka Dot Canvas

By the end of this lab you'll be able to:

• Import the random module and call random.randint() and random.choice()
• Use a fixed random.seed() to make results reproducible
• Write a simple dot-drawing function and call it many times

Two hundred colorful dots scattered across the canvas — each one a random size, color, and position — creating a cheerful, unpredictable canvas every time.

Welcome to the Polka Dot Canvas!

In this lab you'll meet Python's random module — a treasure chest of tools for making programs that behave differently every run! Let's code it together!

How Randomness Works

random.randint(a, b) returns a random whole number between a and b (inclusive). random.choice(list) picks one random item from a list. random.seed(n) fixes the starting point so you always get the same "random" sequence — useful for reproducible demos.

Sample Code

import turtle
import random
monty = turtle.Turtle()
monty.speed(0)
monty.hideturtle()
random.seed(42)

colors = ['red','orange','yellow','green','blue','purple','pink','cyan','coral','gold']

for _ in range(80):
    x = random.randint(-280, 280)
    y = random.randint(-200, 200)
    r = random.randint(8, 40)
    c = random.choice(colors)
    monty.penup()
    monty.goto(x, y)
    monty.dot(r, c)

What Do You Think Will Happen?

random.seed(42) is set before the loop. If you click Reset and Run again, will the dots appear in the same positions or different positions? Make your guess — then click Run twice to find out!

Try It Now

▶ Run ↻ Reset

The dots appear in the same positions every run — because random.seed(42) resets the sequence to the same starting point. Were you right?

How It Works

random.seed(42) doesn't make things less random — it just determines which random sequence you get. Change 42 to any other number and you'll get a completely different (but still reproducible) pattern.

for _ in range(80) uses _ as the loop variable because we don't actually need the counter — we're just repeating 80 times.

Explanation Table

Line	What it does
import random	Load Python's random number module
random.seed(42)	Fix the random sequence for reproducibility
random.randint(-280, 280)	Random integer from -280 to 280 inclusive
random.choice(colors)	Pick one item from the list at random
monty.dot(r, c)	Draw a filled circle of radius r in color c

Learning Check

Spot the Bug!

The program below draws dots but they all appear at the same position! Find and fix the bug — the x and y coordinates should be random, not fixed.

▶ Run ↻ Reset

Replace x = 0 with x = random.randint(-280, 280) and y = 0 with y = random.randint(-200, 200).

Experiments

1. Remove the seed. Delete random.seed(42). Now each run produces a different pattern. You'll know it worked when clicking Run twice gives different arrangements.

2. Change the seed. Try random.seed(99) or random.seed(1). Each seed produces its own unique pattern. You'll know it worked when the dots rearrange completely.

3. Make all dots the same size but random color. Change r = random.randint(8, 40) to r = 20. You'll know it worked when the dots are uniform in size but colorful.

4. Double the count. Change range(80) to range(160). You'll know it worked when the canvas is much more densely packed with dots.

Wonderful Work!

You unlocked the power of randomness in Python — and learned that "random" doesn't have to mean "uncontrolled." Seeds give you the best of both worlds! Up next: Brick Wall — tiling a surface with a function and offset rows.