Lesson 6 reading

The lesson gave you the driver — but a game needs something to chase, and the anatomy table has an empty "objective" row. This reading is the toolkit that fills it: a toolbox called random that lets the computer surprise you, and the turtle functions that measure and decorate. Every one of them is a function call, and most of them hand a value back for you to use — they're the ingredients for next lesson.

randint — both ends included

>>> random.randint(1, 6)
4
>>> random.randint(1, 6)
6
>>> random.randint(1, 6)
1

random.randint(1, 6) is a six-sided die: it can hand back 1, 2, 3, 4, 5, or 6. Notice that's different from range(1, 6), which stops at 5 — randint includes both ends. Two functions, two rules; when a random number seems off by one, this is why.

choice — random meets lists

randint picks a random number. random.choice picks a random item from a list — your Lesson 4 lists, meeting this week's toolbox:

>>> colors = ["red", "orange", "yellow", "green", "blue", "purple"]
>>> random.choice(colors)
'green'
>>> random.choice(colors)
'red'

Anything a list can hold, choice can pick: colors, names, sizes. Perfect for a game that wants variety — a chased dot that respawns wearing a random color, say.

distance — to a turtle, or to a point

t.distance(food) hands back the number of pixels between two turtles — ask your turtle how far it is from another one. distance also takes a plain point:

>>> t.distance(0, 0)
223.606797749979

That's how far the turtle is from the center of the window. Useful question for a game: "has the player wandered too far?" — if t.distance(0, 0) > 300: is an invisible circular fence, built from the same pipeline as the food check: function → number → comparison → boolean → if.

write — words on the window

Until now, words went to the terminal with print. Games put words on the window:

t.write("hello!")

Tiny, isn't it? Give it a font — the name, the size, and a style, wrapped in parentheses as one input:

t.write("GAME ON", font=("Arial", 24, "bold"))

The text appears wherever the turtle is standing, and stays until a clear(). Park a penup turtle in a corner and let it do the writing — that's exactly how the score will work next lesson.

Costumes and sizes

The turtle has six built-in shapes:

t.shape("turtle")    # also: "arrow", "circle", "square", "triangle", "classic"

And a size dial:

food.turtlesize(2)   # twice as big
food.turtlesize(3)   # three times

Here's the game-design secret hiding in that dial: a bigger food is easier to hit, and a bigger < 20 in the food check is easier too. Those two numbers are difficulty knobs. Every game you've ever played has numbers like these inside it, and someone sat there tuning them.

color sets a turtle's whole look in one call:

food.color("hotpink")

Try it

Same rules as always: predict first, then run. Say out loud what will happen before you press Run.

>>> import random
>>> random.randint(10, 10)

(How many possible answers does that one have?)

import turtle
import random

t = turtle.Turtle()
t.penup()

colors = ["red", "orange", "yellow", "green", "blue", "purple"]

for i in range(6):
    t.color(random.choice(colors))
    t.goto(random.randint(-200, 200), random.randint(-200, 200))
    t.write("here!", font=("Arial", 16, "bold"))

turtle.done()

import turtle

t = turtle.Turtle()
t.shape("turtle")
t.turtlesize(3)

print(t.distance(0, 0))
t.forward(100)
print(t.distance(0, 0))

turtle.done()

One habit worth keeping: when a random thing behaves strangely, run it many times before judging — one roll of a die tells you nothing. That's Lesson 2's experiment skill, and with random it's the only way to see the pattern.