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What are variables?

A variable is like a labeled box where you can store information. You give it a name and put a value inside. Later, you can use that name to get the value back. In real life:
  • Your name is a “variable” that stores what people call you
  • Your age is a “variable” that stores a number
  • Your favorite color is a “variable” that stores text
In Python, we create variables to store data our programs need to remember.

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Creating your first variable

Here’s how to create a variable: 
name = "Alice"
age = 25
is_student = True
Let’s break this down:
  • name is the variable name
  • = means “store the value on the right in the variable on the left”
  • "Alice" is the value we’re storing

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Naming rules

Python has rules for variable names: Allowed: 
user_name = "Dave"      # lowercase with underscores (Python style)
userName = "Dave"       # camelCase (works but not Python style)
age2 = 30              # numbers are OK (not at start)
_private = "secret"    # underscore at start is OK
Not allowed: 
2age = 30              # Can't start with number
my-name = "Dave"       # No hyphens (Python thinks it's subtraction)
my name = "Dave"       # No spaces
class = "Python"       # Can't use Python keywords

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Python naming convention

In Python, we use lowercase letters with underscores between words. This is called “snake_case” and it’s the standard way to name variables in Python. 
# Good Python style
first_name = "Alice"
user_age = 25
is_logged_in = True
shopping_cart_total = 49.99

# Avoid camelCase (this is for other languages)
firstName = "Alice"  # Works, but not Python style
userAge = 25
isLoggedIn = True
Use descriptive names for your variables! Instead of x or temp, use names like user_score or file_path. Your future self (and teammates) will thank you when reading the code later.

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Changing variables

Variables can change (that’s why they’re called variables!): 
# Start with one value
score = 0
print(score)  # Shows: 0

# Change it
score = 10
print(score)  # Shows: 10

# Change it again
score = score + 5
print(score)  # Shows: 15

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Common mistakes

# Wrong
name = Alice  # Python looks for a variable called Alice

# Right
name = "Alice"  # This creates text

# Wrong
print(score)  # Error: score doesn't exist yet
score = 10

# Right
score = 10
print(score)  # Now it works

# = means "store"
age = 25

# == means "compare" (we'll learn this later)
if age == 25:
    print("Quarter century!")

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What’s next?

Before we explore data types, let’s learn about comments - a crucial tool for making your code readable.

Comments

Document your code clearly