Understanding Python Variables

A Python variable is a named storage location that holds a value. It allows you to label information with a descriptive name, making it easy to access and modify that data throughout your program.

Think of a variable as a labeled box. You can put a value inside (like the number 42), and whenever you need that number later, you just refer to the box's label (e.g., answer).

Using variables makes your code flexible. Instead of hard-coding values, you use names that make sense to humans, making your code readable and easier to maintain.

How to Create a Variable

In Python, you create a variable through assignment using the equals sign (=). Unlike some other languages, you don't need a special command to declare it first. It happens automatically the moment you assign a value.

• user_name = "Ada Lovelace" (String)
• user_age = 36 (Integer)
• is_programmer = True (Boolean)

Practical Application: Creating Variables

The best way to understand variables is to create them yourself. Let's write some code.

Exercise 1: Assign and Print

Create a variable named greeting with the text "Hello, World!". Then, create a variable named year with the number 2025. Print both of them.

# Define the variables
greeting = "Hello, World!"
year = 2025

# Print them
print(greeting)
print(year)

Your output will appear here...

Exercise 2: Reassigning Variables

Variables are dynamic, their values can change. This is why they are called "variables" (able to vary).

In the box below, create a variable called current_status and set it to "Pending". Print it. Then, on a new line, change the value to "Complete" and print it again to see the update.

current_status = "Pending"
print(f"Status is: {current_status}")

# Reassigning the variable
current_status = "Complete"
print(f"Status is now: {current_status}")

Your output will appear here...

Naming Rules and Best Practices

Python has strict rules and helpful conventions for naming variables. Following these ensures your code runs without errors and is easy for others to read.

• The Rules (Mandatory): Names must start with a letter or underscore (_). They cannot start with a number. They are case-sensitive (age and Age are different).
• The Conventions (Best Practice): Use snake_case. This means using all lowercase letters and separating words with underscores.
• Be Descriptive: Use user_email instead of ue. Clear names act as documentation for your code.

Advanced Concept: Dynamic Typing

Python is dynamically typed. This means you do not need to tell Python what type of data (integer, string, etc.) a variable will hold. Python figures it out automatically.

You can even check what type a variable currently holds using the type() function.

# This is the same code as the prompt.
# Run it to see how the "type" changes!
data = 100
print(type(data)) # 

data = "One Hundred"
print(type(data)) # 

data = True
print(type(data)) # 

Your output will appear here...

Common Mistakes to Avoid

Even experienced developers make these small mistakes:

• Unquoted Strings: Writing name = John causes an error because Python thinks John is another variable. It must be name = "John".
• Case Sensitivity: Calling print(Score) when you defined score (lowercase) will fail.
• Using Keywords: You cannot name a variable if, for, or class, as these are reserved by Python.

Knowledge Check: Apply Your Skills

Let's simulate a simple shopping cart calculation. In the editor below, define variables for:

• An item_name (e.g., "Laptop")
• An item_price (e.g., 500)
• A tax_rate (e.g., 0.10)

Then, create a new variable called total_cost that calculates the price plus tax (Price * Tax Rate + Price). Finally, print a sentence summarizing the order.

# --- Data Variables ---
item_name = "Laptop"
item_price = 1000
tax_rate = 0.05 # 5% tax

# --- Logic / Calculation ---
# We use variables to do the math
tax_amount = item_price * tax_rate
total_cost = item_price + tax_amount

# --- Output ---
print(f"Order: {item_name}")
print(f"Subtotal: {item_price}")
print(f"Tax: {tax_amount}")
print(f"Total Due: {total_cost}")

Your output will appear here...