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Randomness in art: let the computer pick

Real fireworks never burst the same way twice. To paint that, you can't choose every spark yourself. You hand some of the choices to the computer.

The big idea

random_number(low, high) picks a number for you, and pick(list) picks one item from a list, fresh each time they're called.

See it in code

1Start simple

random_number(low, high) gives a whole number between two ends. Use one for x and one for y, and each spark lands somewhere new:

python
spark_count = 40

paper("midnight blue")
for count in range(spark_count):
    dot(x=random_number(20, 380), y=random_number(20, 250), color="white")
rect(x=200, y=365, width=400, height=70, color="black")
Forty sparks in the night sky:
A midnight blue sky scattered with forty small white dots in the top half, above a black harbor.

The y only goes up to 250, so the sparks stay in the sky. The two ends of random_number are how you keep chance inside the lines.

2A step further

pick() chooses from a list that you wrote. That keeps the colors working together while each ring still gets a surprise:

python
ring_count = 12
burst_colors = ["hot pink", "deep sky blue", "gold"]

paper("midnight blue")
for count in range(ring_count):
    ring(x=random_number(40, 360), y=random_number(40, 240), size=random_number(20, 70), color=pick(burst_colors), width=3)
rect(x=200, y=365, width=400, height=70, color="black")
Colors you chose, picked by chance:
A night sky with twelve rings of random sizes in hot pink, deep sky blue, and gold, above a black harbor.

Three things are random now: where each ring goes, how big it is, and its color. The list keeps the picture from turning into a muddle.

3In the paint studio

Where you put a random pick matters. Pick above a loop and the choice is made once. Pick inside it and the choice is made on every trip:

python
burst_count = 2
spark_count = 24
spread = 80
zone_width = 200
burst_colors = ["gold", "orange red", "white"]

paper("midnight blue")
for show in range(burst_count):
    burst_x = show * zone_width + random_number(80, 120)
    burst_y = random_number(90, 190)
    for count in range(spark_count):
        end_x = burst_x + random_number(-spread, spread)
        end_y = burst_y + random_number(-spread, spread)
        line(x1=burst_x, y1=burst_y, x2=end_x, y2=end_y, color=pick(burst_colors), width=2)
        dot(x=end_x, y=end_y, color="white")
rect(x=200, y=365, width=400, height=70, color="black")
Two bursts, one center each, many sparks:
Two fireworks bursts in a night sky, each a spray of thin gold, orange-red, and white lines flying out from its own random center, above a black harbor.

The center is picked once per burst, in the outside loop. Each spark's end is picked in the inside loop, 24 times. So the sparks share a center, and each flies its own way.

The same idea, everywhere

This rule works anywhere chance is used. A game picks a new spot each time a cupcake drops. A bakery program picks a new special each day.

Try it yourself

Move the burst_y line up above the for show line and run it a few times. Both bursts now sit at the same height. Why? Put it back where it was.

The common mistake

Giving random_number its numbers backwards. random_number(380, 20) has nothing to pick from, and the studio tells you to put the smaller number first.

What it unlocks

Random picks are the heart of generative art. In plain Python, the same tools come from the random module, and a list is what pick chooses from.

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