Loops

Loops#

The for Loop#

The for loop – simply put – repeats a command n times:

Example#

The following loop runs 5 times:

for i in range(5):
    print("I'm in a loop!")

This program produces the output:

I'm in a loop!
I'm in a loop!
I'm in a loop!
I'm in a loop!
I'm in a loop!

The Counter Variable#

You can use the variable i as a counter. It increases (starting at 0):

Example#

for i in range(5):
    print(i)

This program prints:

0
1
2
3
4

General Form#

Generally, you write:

for i in range(max):
    <code block>

or

for i in range(min, max):
    <code block>

You can specify how many times the loop runs or define a specific range.

Examples: Drawing with Loops#

You can use loops to draw:

from miniworlds import *

world = World(200, 200)

for i in range(4):
    Circle((20 + 50 * i, 50), 20)

world.run()
circles

Checkerboard Pattern#

Using the modulo operator, you can check if a number is divisible by 2: x is divisible by 2 if x % 2 == 0.

This can be used to create checkerboard-like patterns by combining loops with if statements:

from miniworlds import *

world = World(200, 50)

for i in range(4):
    rect = Rectangle((50 * i, 0), 50, 50)
    if i % 2 == 0:
        rect.color = (255, 0, 0, 255)
    else:
        rect.color = (255, 255, 255, 255)

world.run()
checkers

Graphs#

You can also draw graphs this way:

from miniworlds import *

world = World(400, 400)

for x in range(400):
    gl = 0.5 * x + 50
    y = 400 - gl
    Point((x, y))

world.run()
graphs

Nested Loops#

Using nested loops, you can draw multi-dimensional patterns:

from miniworlds import *

world = World(200, 200)

for i in range(4):
    for j in range(4):
        Circle((20 + 50 * i, 20 + 50 * j), 20)

world.run()
nested loop

The while Loop#

The while loop has the following structure:

while <condition>:
    <code block>

  • As long as the condition is true, the loop repeats. This allows for infinite loops if the condition is never false.

Example#

The following program generates a random pattern:

from miniworlds import *
import random

world = World(255, 60)
x = 0

while x < 255:
    c = Circle((x, 30), 20)
    c.color = (x, 0, 0, random.randint(0, 255))
    x = x + random.randint(10, 50)

world.run()
random color circles

The Main Loop#

Your entire program technically runs inside a while loop:

while <no quit>:
  <draw images on screen>
  <handle logic and events>

The for loop is not suited for this since you need to know ahead of time how many iterations will occur.

Loops Inside Registered Methods#

If you want to use a loop inside an act method or an event handler, keep in mind:

The entire loop is executed within one frame. This means loops are not suitable for controlling animations across frames (like moving a figure frame by frame). Instead, act() is called once per frame.

Example: Traffic Light#

A traffic light system can be modeled as a state diagram:

stateDiagram
    [*] --> Green

    Green --> GreenYellow
    GreenYellow --> Red
    Red --> RedYellow
    RedYellow --> Green

Translated to code with a while loop:

from miniworlds import *

state = "green"

while True:
    if state == "green":
        state = "green-yellow"
        print("green")
    elif state == "green-yellow":
        state = "red"
        print("green-yellow")
    elif state == "red":
        state = "red-yellow"
        print("red")
    elif state == "red-yellow":
        state = "green"
        print("red-yellow")

world.run()

In a miniworlds program, this becomes part of the act() method:

from miniworlds import *

world = World(100, 240)
state = "green"
g = Circle((50, 40), 40)
y = Circle((50, 120), 40)
r = Circle((50, 200), 40)

@world.register
def act(self):
    global state
    if world.frame % 20 == 0:
        if state == "green":
            g.color = (0, 255, 0)
            y.color = (255, 255, 255)
            r.color = (255, 255, 255)
            state = "green-yellow"
            print("green")
        elif state == "green-yellow":
            g.color = (0, 255, 0)
            y.color = (255, 255, 0)
            r.color = (255, 255, 255)
            state = "red"
            print("green-yellow")
        elif state == "red":
            g.color = (255, 255, 255)
            y.color = (255, 255, 255)
            r.color = (255, 0, 0)
            state = "red-yellow"
            print("red")
        elif state == "red-yellow":
            g.color = (255, 255, 255)
            y.color = (255, 255, 0)
            r.color = (255, 0, 0)
            state = "green"
            print("red-yellow")

world.run()
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