🐢 Python Turtle - Cheat Sheet & Wiki

A quick overview of all important commands and rules from the Python course.

📚 Algorithm Fundamentals

Definition: Algorithm

An algorithm is a set of instructions for solving a task or a set of tasks.

Properties of Algorithms

• Executability: The algorithm should be executable without errors
• Finiteness: The algorithm has finite length
• Repeatability: Same inputs produce same outputs
• Determinism: For each step there is exactly one defined next step

🚀 Basics - Always First!

import turtle
t = turtle.Turtle()
t.speed(5)  # 1:slowest, 3:slow, 5:normal, 10:fast, 0:fastest

🎨 Turtle Commands

Command	What Happens	Example
t.forward(number)	Tobi goes forward	t.forward(100)
t.backward(number)	Tobi goes backward	t.backward(50)
t.right(degrees)	Tobi turns right	t.right(90)
t.left(degrees)	Tobi turns left	t.left(45)
t.circle(radius)	Tobi draws a circle	t.circle(30)
t.goto(x, y)	Tobi jumps to position	t.goto(100, 50)
t.penup()	Lift pen (don't draw)	t.penup()
t.pendown()	Lower pen (draw)	t.pendown()
t.color("color")	Change color	t.color("red")
t.write("text")	Write text	t.write("Hello!")
t.heading()	Get current direction (0-360°)	if t.heading() == 90:

📊 Variables & Container Model

Variables are containers for values from which you can take something out and put something in.

Rule	Explanation	Example
Create	name = value	age = 15
Overwrite	New value with =	age = 16
Calculate	Variable = old Variable + number	age = age + 1
Names	Lowercase, self-explanatory, no spaces	shoe_size = 42

Data Types

Type	What it is	Example	Convert
Integer	Whole number	x = 5	int("5")
Float	Decimal number	y = 3.14	float("3.14")
String	Text	name = "Max"	str(5)
Boolean	True/False	win = True	-

Casting (Conversion)

# String to number
age = int(input("Age: "))        # to Integer
height = float(input("Height: "))    # to Float

# Number to string
message = "I am " + str(25) + " years old"

🔢 Arithmetic Operators

Operator	Name	Example	Result
+	Addition	5 + 3	8
-	Subtraction	5 - 3	2
*	Multiplication	5 * 3	15
/	Division	10 / 3	3.333...
//	Integer Division	10 // 3	3
%	Remainder (Modulo)	10 % 3	1
**	Power	2 ** 3	8

✅ Conditions & Branching

Comparison Operators

Operator	Meaning	Example
==	equals	if x == 5:
!=	not equal	if x != 5:
<	less than	if x < 5:
<=	less than or equal	if x <= 5:
>	greater than	if x > 5:
>=	greater than or equal	if x >= 5:

Logical Operators

Operator	Meaning	Example
and	AND (both must be true)	if x > 0 and x < 10:
or	OR (one must be true)	if x < 0 or x > 10:
not	NOT (reverses)	if not (x == 5):

If-Structures

# Simple condition
if condition:
    # Executed when true
    t.write("True!")
else:
    # Executed when false
    t.write("False!")

# Multiple conditions
if x < 0:
    t.write("Negative")
elif x == 0:
    t.write("Zero")
else:
    t.write("Positive")

🔄 Loops

For-Loop (specific number)

for i in range(5):          # 0, 1, 2, 3, 4
    t.forward(10)

for i in range(2, 8):       # 2, 3, 4, 5, 6, 7
    t.write(i)

for i in range(0, 10, 2):   # 0, 2, 4, 6, 8 (step size 2)
    t.circle(i)

Range Variants

• range(5): 0 to 4
• range(2, 8): 2 to 7
• range(0, 10, 2): 0, 2, 4, 6, 8 (steps of 2)

While-Loop (as long as condition is true)

x = 0
while x < 5:
    t.forward(x)
    x = x + 1

Important

• Always colon after condition/loop: :
• Content must be indented (Tab key)
• With while-loops: Change variable, otherwise infinite loop!

💬 User Input

Command	What Happens	Example
input("text")	User enters text	name = input("Your name: ")
int(input())	Convert input to number	age = int(input("Age: "))
float(input())	Convert input to decimal	height = float(input("Height: "))

Important Note

input() always returns a string! For calculations you must cast:

# Wrong:
age = input("Age: ")  # String!

# Right:
age = int(input("Age: "))  # Integer!

⚙️ Functions

Simple Function

def my_function():
    t.forward(50)
    t.left(90)

# Call:
my_function()

Function with Parameters

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

# Call:
square(50)

Function with Multiple Parameters

def rectangle(width, height):
    for i in range(2):
        t.forward(width)
        t.left(90)
        t.forward(height)
        t.left(90)

# Call:
rectangle(80, 40)

Function with Return Value

def add(a, b):
    result = a + b
    return result

# Use:
sum = add(5, 3)
t.write(sum)

📚 Important Libraries

Random (Random Numbers)

import random

# Random integer between 1 and 6
dice = random.randint(1, 6)

# Random element from list
colors = ["red", "blue", "green"]
color = random.choice(colors)

# Random decimal between 0 and 1
random_num = random.random()

Math (Mathematics)

import math

# Use Pi
circumference = 2 * math.pi * radius

# Square root
root = math.sqrt(25)  # = 5.0

# Power
power = math.pow(2, 3)  # = 8.0

⚠️ Common Errors

Error	Correct	Wrong
Forgot colon	if x == 5:	if x == 5
Forgot indentation	t.forward(10)	t.forward(10)
= instead of ==	if x == 5:	if x = 5:
String + Number	"Age: " + str(15)	"Age: " + 15
Capitalization	True	true
Variable before assignment	x = 5 then print(x)	print(x) then x = 5

🎯 Useful Tricks

String Formatting

name = "Max"
age = 15
t.write(f"Hello {name}, you are {age} years old!")

Lists

numbers = [1, 2, 3, 4, 5]
colors = ["red", "blue", "green"]

# First element: list[0]
first_number = numbers[0]  # = 1

# Go through list:
for color in colors:
    t.color(color)
    t.circle(20)

Multiple Turtle Objects

import turtle

tobi = turtle.Turtle()
lisa = turtle.Turtle()

tobi.color("red")
lisa.color("blue")

tobi.forward(100)
lisa.backward(100)

🔧 Debugging Tips

1. Print-Debugging: Use print() to check variable values

x = 10
print(f"x has the value: {x}")

2. Step by step: Test small parts individually

3. Use comments: Explain difficult parts

# Here the square is drawn
for i in range(4):
    t.forward(50)
    t.left(90)

4. Common problems:
   • Forgotten colons
   • Wrong indentation
   • = instead of ==
   • Infinite loops with while

🎨 Geometric Pattern Examples

Spiral

for i in range(50):
    t.forward(i * 2)
    t.left(90)

Star (5-pointed)

for i in range(5):
    t.forward(100)
    t.right(144)

Concentric Circles

for i in range(1, 6):
    t.circle(i * 20)
    t.penup()
    t.right(90)
    t.forward(20)
    t.left(90)
    t.pendown()

📋 Project Planning Tips

1. Plan first: Think about the flow before you code
2. Small steps: Program in small, testable sections
3. Test frequently: Run your program regularly
4. Comment: Explain difficult parts in the code
5. Ask for help: Don't struggle alone too long with problems

📝 Quick Template

import turtle
import random
import math

t = turtle.Turtle()
t.speed(5)

# Your code here

# Keep window open (at the end):
turtle.done()

🏆 Evaluation Criteria

For projects, the following is evaluated:

• Functionality: Does the program run without errors?
• Code Quality: Clean structure and comments?
• Concept Usage: Meaningful use of functions, loops, etc.?
• Creativity: Own ideas and extensions
• Problem Solving: How are challenges solved?