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Module

Data & Variables

What regular data types do we worry about in programming? We'll focus on each type, when to use it, and then store them in variables.

1. data types

Python's Core Data Types

Every value in a program has a type— it tells Python how much memory to set aside and what operations are allowed on that value. You don't have to declare types yourself; Python figures them out automatically when you write a value.

The main types you'll use in Python are:

  • int — whole numbers: 42, -7, 0
  • float — decimal numbers: 3.14, -0.5, 2.0
  • str — text (string): "hello", 'world'
  • bool — truth values: True or False

Every type in one snippet:

age        = 25           # int
price      = 9.99         # float
name       = "Ada"        # str
is_student = True         # bool

Question 1 of 5

What data type is the value `3.14` in Python?

2. use cases

When to Use Each Type

Choosing the right type makes your code clearer and easier to reason about. Here are the best-fit uses for each regular type, plus a simple example you could see in a real program:

  • int — counting whole items (no decimals).
  • float — measurements or values with decimals.
  • str — names, labels, and text.
  • bool — yes/no or true/false conditions.

Use cases in code:

num_students  = 28         # int
temperature_c = 21.5       # float
welcome_text  = "Hello!"   # str
is_logged_in  = False      # bool

3. variables

Storing Values in Variables

A variable is a named container for a value. You create one with an assignment statement:

name = value

Unlike some languages, Python requires no keyword like let or var. Assigning to an existing name simply replaces the stored value — variables can even change type between assignments.

The built-in type() function tells you the type of any value or variable:

Creating, re-assigning, and inspecting variables:

# Create a variable
score = 100

# Re-assign it
score = 42
print(score)        # 42

# Check its type
print(type(score))  # <class 'int'>

# A variable can change type
score = "pending"
print(type(score))  # <class 'str'>

Question 1 of 5

What type does `x = 42` create?

4. naming

Naming Conventions

Python doesn't enforce names — technically x = 42 and user_age = 42both work. But good names make code readable at a glance. Python's community follows PEP 8, which recommends:

  • Use snake_case for variable names: all lowercase, words separated by underscores (first_name, total_price).
  • Be descriptive — user_age beats a or x1.
  • Names must start with a letter or underscore — not a digit.
  • Names are case-sensitive: Score, score, and SCORE are three different variables.
  • Avoid Python's reserved keywords (if, for, True, etc.) as variable names.

Good names vs. bad names:

# ✗ Hard to read
a = 25
x1 = "Ada Lovelace"
TotalPrice = 9.99

# ✓ Clear and conventional
user_age   = 25
full_name  = "Ada Lovelace"
total_price = 9.99

Question 1 of 4

Which variable name follows Python's snake_case convention?

5. project

First Program

Put everything together by writing and running your first Python script. You'll install Python, create a file, declare a string variable, and print it to the console.

First Program

  1. 1.Install Python from python.org (choose the latest stable release and check 'Add Python to PATH' during setup).
  2. 2.Create a new file called hello.py in any folder on your computer.
  3. 3.Open hello.py in a text editor and type: greeting = "Hello, World!" then on the next line: print(greeting)
  4. 4.Open a terminal (Command Prompt / Terminal), navigate to the folder containing hello.py, and run: python hello.py — you should see Hello, World! printed.