Variables and Primitive Types

beginner level · ~12 min · Module 2: Variables and Data Types

Learn how to declare variables, understand Python primitive types, and convert between types.

Learning objectives

  • Declare variables using snake_case naming conventions
  • Identify integers, floats, strings, booleans, and NoneType
  • Use type() and type casting functions (int(), float(), str(), bool())

Lesson material

Declaring Variables

A variable is a named container holding a value in memory. In Python, assignment is done with the = operator.

Python Naming Conventions (PEP 8):

  • Use snake_case for variable and function names.
  • Variable names must start with a letter or underscore, NOT a number.
  • Names are case-sensitive (age vs Age).

Example code

# Variable declarations
user_name = "Alice"   # str
user_age = 25         # int
account_balance = 199.99 # float
is_active = True      # bool
middle_name = None    # NoneType

print(f"{user_name} is {user_age} years old.")
print("Type of user_age:", type(user_age))

Type Conversion (Casting)

You can convert values between types using built-in constructors:

  • int("10") -> 10
  • float("3.14") -> 3.14
  • str(100) -> "100"
  • bool(1) -> True (0, "", None, [], {} evaluate to False)

Example code

num_str = "42"
num_int = int(num_str)
print(num_int + 8)

Practice exercise: Variable Math and Casting

Create a variable `age_str` with value `"20"`. Cast it to an integer, add 5 to it, and print the result.

Test yourself with the Module 2: Variables and Data Types quiz →

View the full Python curriculum →