Python Lesson 4: Variables

A variable is a labeled box that stores data. You give it a name, put something in it, and use that name later to access the value.

Creating Variables

name = "Alice"
age = 25
height = 5.6
is_student = True

print(name)    # Alice
print(age)     # 25
print(height)  # 5.6

Naming Rules

• Use letters, numbers, underscores: user_name, age2
• Start with a letter or underscore: _data, score
• Cannot start with a number: 2name is an ERROR
• No spaces: use first_name not “first name”

Python Style: snake_case

# Good Python style (snake_case)
first_name = "Bob"
total_score = 100
user_email = "bob@example.com"

# Works but not Pythonic (camelCase)
firstName = "Bob"  # avoid this in Python

Changing Variable Values

score = 0
print(score)    # 0

score = 10
print(score)    # 10

score = score + 5
print(score)    # 15

Multiple Assignment

# Same value to multiple variables
x = y = z = 0

# Different values in one line
name, age, city = "Alice", 30, "London"
print(name, age, city)  # Alice 30 London