Python Variables

Variables are how programs store information. A variable is a name that points to a value in memory.

The key idea:

• You create a variable by assigning a value to it with =

Create variables

name = "John"
age = 25
city = "New York"
is_student = True

print(name)
print(age)
print(city)
print(is_student)

Expected output:

John
25
New York
True

What assignment really means

In Python, = means “make this name refer to this value”.

a = 10
b = a
a = 20

print(a)
print(b)

Expected output:

20
10

This shows that b kept the old value. Python does not “link” them in this simple example.

Naming rules (do this from day 1)

Good names tell the reader what the data represents.

✅ Good:

total_price = 120.50
user_email = "john@example.com"
items_in_cart = 3

❌ Poor:

x = 120.50
temp = "john@example.com"
n = 3

Python naming style

Python developers mostly use snake_case:

• user_name
• total_cost
• is_active

Updating variables

score = 0
print(score)

score = 10
print(score)

score = score + 5
print(score)

Expected output:

0
10
15

Graph: name to value

flowchart LR
  A[name] --> B["John"]
  C[age] --> D[25]
  E[score] --> F[15]

One concept that prevents bugs

If you see wrong output, check:

• What value is stored?
• Where did it change?
• What line updated it?

That thinking makes debugging easier.

In the next lesson, you will learn data types so you understand what kind of values Python variables can hold.