Variables & Data Types

Variables are the building blocks of any program. In this lesson, you will learn how to store data, what types of data exist, and how to differentiate between mutable and immutable objects.

What are Variables?

In many languages, variables are like boxes that hold values. In Python, it's more accurate to think of them as labels attached to objects in memory.

Variable Naming Rules

✅ Valid Names

❌ Invalid Names

# These will cause errors:
# 2users = 10        # Cannot start with number
# user-name = "Bob"  # No hyphens
# class = "Math"     # Cannot use keywords
# user name = "Sue"  # No spaces

Naming Conventions

Python Data Types

1. Numbers

Integers (int)

Floats (float)

2. Strings (str)

3. Booleans (bool)

4. None Type

5. Lists (list)

Ordered, mutable collections of items.

6. Tuples (tuple)

Ordered, immutable collections. Once created, they cannot be changed.

7. Dictionaries (dict)

Ordered collections of key-value pairs (preserves insertion order as of Python 3.7+).

8. Sets (set)

Unordered collections of unique items.

9. Bytes (bytes)

Immutable sequences of single bytes.

Mutability vs Immutability

This is a key concept in Python.

• Immutable: The value cannot be changed. If you change it, Python creates a new object. (int, float, bool, str, tuple)
• Mutable: The value can be changed in place. (list, dict, set)

Type Checking

Type Conversion (Casting)

Quiz

Key Takeaways

✅ Variables are labels for data in memory.
✅ Basic types (int, float, str, bool) are immutable.
✅ Use type() to check data types.

What's Next?

In the next lesson, we'll learn about Operators & Expressions to perform calculations and logic.

Keep coding! 🚀