Variables & Data Types

Variables — Labeled Boxes

A variable is like a labeled box in the warehouse of your computer. You write on it what's inside (name), throw something in ("Max"), and can find it later via the label.

In JavaScript, you created variables with let or const. In Python, you don't need any keyword — just name, equals sign, value. Done.

# Python — einfach und direkt
name = "Max"
alter = 16
pi = 3.14159
spieler_aktiv = True

name = "Max"
alter = 16

let name = "Max";
let alter = 16;

The 4 Data Types You Need to Know

Python recognizes the data type automatically. You don't have to declare anything. But you should know which types exist:

• str (String): Text in quotes — "Hallo"
• int (Integer): Whole numbers — 42
• float (Floating Point): Decimal numbers — 3.14
• bool (Boolean): True/False — True or False

With type(), you can check at any time which type is inside a variable.

name = "Python"
alter = 30
groesse = 1.75
aktiv = True

print(type(name))    # <class 'str'>
print(type(alter))   # <class 'int'>
print(type(groesse)) # <class 'float'>
print(type(aktiv))   # <class 'bool'>

Type Conversion — When Python Doesn't Play Along

Sometimes you need to convert one type into another. Example: input() always returns a string. If you want to calculate with it, you first have to convert it to int or float.

This is called Type Casting — in Python with int(), float(), str(), or bool().

# input() liefert immer einen String!
alter_text = "16"

# So geht es NICHT:
# alter_text + 5  → Fehler!

# So geht es RICHTIG:
alter_zahl = int(alter_text)
print(alter_zahl + 5)   # 21

# Und zurück:
preis = 19.99
preis_text = str(preis)
print("Der Preis ist: " + preis_text)

zahl = int("16")
text = str(19.99)

let zahl = parseInt("16");
let text = String(19.99);

Variables in Action: Gaming Example

Imagine you're programming a small RPG. Every player has values that change — variables are perfect for exactly that.

# Spieler-Status in einem RPG
spieler_name = "DragonSlayer99"
level = 5
hp = 100
mana = 50.5
ist_online = True

print(f"  Spieler: {spieler_name}")
print(f" Level: {level}")
print(f"  HP: {hp}")
print(f" Mana: {mana}")
print(f" Online: {ist_online}")

# Level-Up!
level = level + 1
hp = hp + 20
print(f" Level-Up! Du bist jetzt Level {level}!")

Good Names — The Art of Variable Names

In Python, there are conventions for variable names. They help you and others read the code. Here are the most important rules:

• Only lowercase letters, numbers, and underscores: spieler_name
• No numbers at the beginning: 1name is forbidden
• No spaces — use underscores instead: mein_name
• Be descriptive: alter instead of a
• No reserved words: print, if, for are off-limits

This is called snake_case — the Python standard notation.

#  Gute Namen
spieler_name = "Max"
aktuelles_level = 42
ist_angemeldet = True

#  Schlechte Namen
# x = "Max"        → zu kurz
# 1name = "Max"    → Zahl am Anfang
# mein Name = "Max" → Leerzeichen!
# print = 5        → reserviertes Wort!