Variables Data Types and Operators

Variables Data Types and Operators#

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Variables#

Python uses variables to store information that can be used later in a program. Think of a variable as a name tag attached to an object in memory — not the box itself, but the label stuck onto it.

🧱 Creating Variables#

A variable is created when you assign a value to a name using the = sign.

`

You can later use these variables anywhere in your program:

🎯 What Really Happens in Memory#

When you write:

Python creates an object (10) in memory, and x is just a reference (a label) that points to that object.

If you do this:

Now both x and y point to the same object in memory.

✅ The id() function shows that both have the same ID, meaning they point to the same memory location.

Variable

Points To

Object Value

x

👉

10

y

👉

10 (same object as x)

Now, if you change the object:

❗ y still points to the old object (10), because you changed what x points to, not the object itself.

💡 Analogy#

Think of x and y as name tags stuck to a coffee mug. Both can point to the same mug ☕, but if x changes its tag to a new mug, y still remains attached to the old one.

Variables#

A variable is created when you assign a value to a name using the = sign.

`

You can later use these variables anywhere in your program.

✅ Naming Rules

  • Must start with a letter or underscore (_)

  • Can contain letters, numbers, and underscores

  • Case-sensitive (name ≠ Name)

  • Avoid using keywords like for, if, class, etc.

🧮 Data Types#

Every value in Python has a type.

Data Type

Example

Description

int

10

Whole numbers

float

3.14

Decimal numbers

str

"Python"

Text or characters

bool

True, False

Logical values

list

[1, 2, 3]

Ordered, changeable collection

tuple

(1, 2, 3)

Ordered, unchangeable collection

dict

{"name": "Alex", "sales": 200}

Key-value pairs

You can check a variable’s type with the built-in type() function.

⚙️ Operators in Python#

Operators perform operations on variables and values.

Arithmetic Operators#

Operator

Description

Example

+

Addition

10 + 5 → 15

-

Subtraction

10 - 3 → 7

*

Multiplication

4 * 2 → 8

/

Division

8 / 2 → 4.0

%

Modulus (Remainder)

9 % 2 → 1

**

Exponent

2 ** 3 → 8

Comparison Operators#

Operator

Meaning

Example

==

Equal to

5 == 5 → True

!=

Not equal to

5 != 3 → True

>

Greater than

10 > 5 → True

<

Less than

2 < 8 → True

Logical Operators#

Operator

Description

Example

and

True if both are True

(5 > 2 and 4 < 10) → True

or

True if one is True

(5 > 2 or 4 > 10) → True

not

Reverses result

not (5 > 2) → False

🔁 Type Conversion#

You can change one data type to another using:

Why Naming Conventions Exist#

Good naming makes code easier to read, debug, and share. Python follows certain rules and best practices:

  • Variable names cannot be Python keywords (like class, if, for).

  • They must start with a letter or underscore (_), not a number.

  • They are case-sensitive (Name ≠ name).

These conventions help both humans and computers understand the code clearly!

Why You Can't Use Words Like class or if

These are reserved keywords — Python uses them for its own syntax. For example:

`

❌ This gives a SyntaxError because class is already used to define classes in Python.

✅ Instead, use:

🧠 Quick Practice Questions#

  • What is the difference between a variable and an object in Python?

  • What will this code print and why?

  • Predict the output:

  • Create variables to store:

  • Your name, age, monthly income, and whether you are a student. Then print them in one line using:

  • Write a Python program that:

  1. Takes two numbers a and b.

  2. Prints their sum, difference, and product.

Example:

  • Predict the output without running the code:

  • Which of the following are valid variable names? a) 2price  b) _price  c) class  d) price2

  • Predict the output:

  • Identify the data types:

  • Find a reserved keyword using keyword.kwlist and try using it as a variable. What error do you get? Replace it with a meaningful name.

  • Write a short Python snippet that calculates profit margin using variables with clear business-style names (cost_price, selling_price, profit_margin).

# Your code here
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