Goals

• Import and use external libraries
• Define and use your own functions
• Understand parameters and return values
• Structure programs cleanly

External Libraries

Python becomes even more powerful through libraries. A library is a collection of functions that other programmers have written.

The random Library

import turtle
import random  

t = turtle.Turtle()

# Generate random numbers
random_number = random.randint(1, 6)  
t.write(f"Dice: {random_number}")

t.penup()
t.goto(0, -50)
t.pendown()

# Random color
colors = ["red", "blue", "green", "yellow", "purple"]
random_color = random.choice(colors)  
t.color(random_color)
t.circle(30)

The math Library

import turtle
import math  

t = turtle.Turtle()

# Use mathematical functions
radius = 50
circumference = 2 * math.pi * radius  
area = math.pi * radius * radius  

t.write(f"Circle: Circumference = {circumference:.1f}")
t.penup()
t.goto(0, -30)
t.pendown()
t.write(f"Area = {area:.1f}")

Useful Functions

random Library:

• random.randint(a, b): Random integer between a and b
• random.choice(list): Random element from a list
• random.random(): Random decimal between 0 and 1

math Library:

• math.pi: The number Pi (3.14159...)
• math.sqrt(x): Square root of x
• math.pow(x, y): x to the power of y

Defining Functions

You already know many functions: t.forward(), t.left(), int(), etc. Functions give you the ability to reuse program code in different places with little effort.

Simple Functions without Parameters

import turtle
t = turtle.Turtle()

def draw_triangle():  
    for i in range(3):   
        t.forward(50)    
        t.left(120)      

# Call function
draw_triangle()
t.forward(100)
draw_triangle()

Explanation

With def we define a new function called draw_triangle. The code in the function is only executed when we call it with draw_triangle().

Functions with Parameters

import turtle
t = turtle.Turtle()

def draw_square(size):  
    for i in range(4):          
        t.forward(size)      
        t.left(90)              

# Draw different squares
draw_square(30)
t.penup()
t.forward(100)
t.pendown()
draw_square(50)

Functions with Return Values

import turtle
t = turtle.Turtle()

def square_perimeter(side_length):  
    perimeter = side_length * 4
    return perimeter                  

# Use function
side = 25
perimeter = square_perimeter(side)
t.write(f"Perimeter: {perimeter}")

Tasks

Task 1: Star Function

Write a function draw_star(size) that draws a 5-pointed star.

Task 2: Random Artwork

Create a program that draws random artwork:

• Draw 10 circles with random sizes (between 10 and 50)
• Each circle should have a random color
• The position of each circle should be random
• Use a function random_circle()

Task 3: Polygon Generator

Create a function draw_polygon(sides, size) that draws any regular polygon.

Task 4: Geometry Calculator

Write functions for geometric calculations:

• circle_area(radius): Calculates the area of a circle
• rectangle_perimeter(width, height): Calculates the perimeter of a rectangle

Preparation for Block 6

Think about more complex programs that combine all previous concepts.