Python · Quick Reference

Lesson 2 — Variables & Data Types Cheat Sheet

Python

In one line: A variable is a named container that stores a value in your computer's memory. You give it a name, assign a value with =, and from that point on you can use that name anywhere i...

Key Ideas

1What is a Variable?. A variable is a named container that stores a value in your computer's memory. You give it a name, assign a value with =, and from that point on you can use that name ...

2Naming Rules & Best Practices. Variable names must follow specific rules, and following good conventions makes your code professional and readable.

3Python's Core Data Types. Every value in Python has a type. The five most important types you'll use every day are:

4Checking Types with type(). Python's built-in type() function tells you exactly what type a variable or value is. This is incredibly useful for debugging — especially when a program isn't behavin...

5Type Conversion (Casting). Sometimes you need to convert a value from one type to another. For example, user input is always a string — if you want to do maths with it, you must convert it to in...

Code Examples

# Creating variables — just use = (no keyword needed!)
name = "Aisha"        # stores a text value
age = 17             # stores a whole number
gpa = 3.85           # stores a decimal number
is_enrolled = True  # stores True or False

# Using variables
prin...

# ✅ VALID variable names
student_name = "Ali"
total_marks = 450
_private = "hidden"
score2 = 99

# ❌ INVALID — Python will throw a SyntaxError
# 2score = 99      (starts with number)
# my-score = 99    (hyphen not allowed)
# my score = 99    (space not allo...

# int — whole numbers
students = 30
temperature = -5
big_number = 1_000_000   # underscores allowed for readability

# float — decimal numbers
price = 19.99
pi = 3.14159
scientific = 2.5e6       # scientific notation = 2,500,000.0

# str — text (single or d...