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  • - What Are Variables?
  • - How Assignment Works
  • - Variable Naming Rules
  • - Naming Conventions (Best Practice)
  • - Multiple Assignments
  • - Constants in Python
  • - Mini Project Step

4. Variables and Naming Conventions

Level: BeginnerDuration: 24m

What Are Variables?

Variables are like containers used to store information in your program. You give them a name, assign them a value, and then use them later.

python
message = "Welcome to Python!"
score = 100
pi = 3.14
đź’ˇ Think of variables as labeled boxes where you store data.

How Assignment Works

The equals sign `=` assigns a value to a variable. You can change the value at any time.

python
status = "online"
print(status)  # online
status = "offline"
print(status)  # offline

Variable Naming Rules

  • Variable names must start with a letter or underscore (_)—not a number.
  • Use only letters, numbers, and underscores (no spaces or symbols).
  • Names are case-sensitive (`age` ≠ `Age`).
  • Don’t use Python keywords like `class`, `for`, `if`.
Valid NamesInvalid Names
name, total_price, _count2name, first-name, class
user_name, is_activeuser name, total$for

Naming Conventions (Best Practice)

Writing clean code starts with using meaningful variable names. Follow Python’s style guide (PEP 8):

  • Use snake_case: `user_age`, `total_amount`
  • Use descriptive names: `price_per_item` (not `ppi`)
  • Booleans should sound like True/False: `is_valid`, `has_access`
python
# Good
user_name = "Grace"
is_logged_in = True

# Bad
x = "Grace"
flag = True

Multiple Assignments

Python allows assigning multiple variables in one line.

python
x, y, z = 10, 20, 30
name = city = "Lagos"  # same value for multiple variables

Constants in Python

Python doesn’t have true constants, but by convention, variables written in UPPERCASE are treated as constants.

python
PI = 3.14159
MAX_CONNECTIONS = 5

Mini Project Step

Add a new file called bank_account.py. Create variables for account holder name, account number, account balance, and bank name. Follow Python naming conventions and print the values in a formatted sentence.