What is a variable in Python?

In Python, a variable is a name that refers to a value stored in memory.
It lets you store, reuse, and change data while your program runs.

Simple example

age = 25
name = "Mohi"
price = 99.50

Here:

• age stores an integer (25)
• name stores a string ("Mohi")
• price stores a float (99.50)

Key points about Python variables

1. No type declaration needed

   x = 10      # integer
   x = "ten"   # now a string
   

   Python decides the type automatically.

2. Variables are case-sensitive

   Age = 20
   age = 25
   

   Age and age are different variables.

3. Must start with a letter or underscore
   ✔ Valid:

   total = 100
   _count = 5
   

   ✘ Invalid:

   1total = 100
   

4. Cannot use Python keywords

   # invalid
   class = 10
   

Why variables are important

• Store user input
• Perform calculations
• Make programs readable and flexible

Example:

length = 10
width = 5
area = length * width
print(area)

How is it used to store data?

A Python variable stores data by creating a name that points to a value in the computer’s memory.
Think of it as labeling a box so you can find and use what’s inside later.

Step-by-step: how data is stored

1️⃣ Assignment (=)

x = 10

What happens internally:

• Python creates the value 10 in memory
• The name x is linked (points) to that value

x ───▶ 10

2️⃣ Using the stored data

print(x)

Python:

• Looks up what x points to
• Retrieves 10
• Prints it

3️⃣ Storing different data types

name = "Rice"
price = 45.75
available = True

name ───▶ "Rice"
price ──▶ 45.75
available ─▶ True

Each variable points to a different type of data.

4️⃣ Changing stored data

x = 10
x = 20

Now:

x ───▶ 20

The variable name stays the same, but it points to a new value.

5️⃣ Variables can store results of calculations

length = 8
width = 5
area = length * width

area ───▶ 40

6️⃣ Variables can store user input

crop = input("Enter crop name: ")

Whatever the user types is stored in crop.

Important concept (simple version)

• Variables don’t “contain” data
• They reference (point to) data in memory

This is why you can do:

a = 10
b = a

Both a and b point to the same value:

a ─┐
   └──▶ 10
b ─┘

Real-life example (business/agriculture)

crop_name = "Wheat"
yield_kg = 2500
price_per_kg = 35

total_value = yield_kg * price_per_kg

Here, variables store farm data so Python can calculate, analyze, and report results.

• What is Python?
• How Python manages memory behind the scenes?