Variables and Naming Variables in Python

Python

Learn Python Programming: A Beginner’s Guide to Coding, Automation, and Data Science

 

What is a Variable? 

Imagine you have a magical box where you can store things. You give it a name, put something inside, and later, you can open it to retrieve the item. That’s exactly what a variable does in Python!

A variable is like a labeled container that holds data.

Example:

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

Here, we stored:

• A string ("Alice") in name
• An integer (25) in age
• A float (5.6) in height
• A boolean (True) in is_happy

You can imagine them as:

name  →  Alice
age   →  25
height →  5.6
is_happy → True

Rules for Naming Variables 

Python has some rules (and some best practices) for naming variables. You don’t want to upset Python—it will throw errors at you! 

Valid Variable Names:

• Can contain letters, numbers, and underscores (_) 
• Must start with a letter or an underscore (_), not a number 
• Case-sensitive (age and Age are different!) 
• Should be descriptive (avoid x = 10, use score = 10 instead!)

my_variable = 42  # Valid
_name = "Bob"      # Valid
user2 = "Charlie"  # Valid

Invalid Variable Names:

• Cannot start with a number 
• Cannot use spaces
• Cannot use special characters like @, #, !, -, etc. 
• Cannot be a Python keyword (if, else, for, etc.)

2name = "Oops"   #  ERROR
user-name = "Nope"  #  ERROR
def = 100       #  ERROR (def is a reserved keyword)

Best Practices for Naming Variables 

Since Python won’t physically stop you from writing ugly variable names, here are some golden rules to keep your code clean:

Use Snake Case (snake_case) 

first_name = "John"  #  Easy to read
user_age = 30         #  Descriptive

Avoid Camel Case (camelCase) in Python (It’s more common in JavaScript)

firstName = "John"  #  Not Pythonic (but still works)

Use Meaningful Names

Bad example:

x = 10  #  What is x?
y = 20  #  What is y?

Good example:

apple_price = 10  #  Now we know what this value represents!
total_students = 20  #  Clear meaning

Changing Variable Values 

Variables are not permanent—you can change their values anytime!

mood = "Happy"
print(mood)  # Output: Happy

mood = "Sleepy"
print(mood)  # Output: Sleepy 

You can also swap variables easily:

a, b = 5, 10
print(a, b)  # Output: 5 10

a, b = b, a  # Swap values!
print(a, b)  # Output: 10 5

Conclusion 

• Variables store data like numbers, text, and more.
• Follow naming rules to avoid Python’s angry red error messages.
• Use snake_case for clean and readable code.
• Choose meaningful variable names so future-you understands what’s going on!

Now go forth and create awesome variables in Python!