Variables in Python (CBSE Class 11 Computer Science)

A variable is one of the most important concepts in programming. Whenever a program needs to store information such as a student's name, marks, salary, or age, it uses variables. Variables allow programs to store data temporarily in the computer's memory so that it can be processed whenever required.

Learning Objectives

• Understand variables.
• Learn variable assignment.
• Know the rules for naming variables.
• Understand dynamic typing.
• Learn multiple assignment.
• Learn swapping of variables.

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What is a Variable?

A variable is a named memory location used to store data. The value stored in a variable can change during program execution.

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Variable Representation

Variable Name
      │
      ▼
+-------------+
|   marks     |
+-------------+
|     95      |
+-------------+

Here, marks is the variable name and 95 is the value stored in it.

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Creating Variables

In Python, a variable is created automatically when a value is assigned to it. No separate declaration is required.

Syntax

variable_name = value

Examples

name = "Aman"

age = 17

marks = 92.5

passed = True

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Assignment Operator (=)

The assignment operator (=) assigns the value on the right side to the variable on the left side.

x = 50

Here, the value 50 is assigned to the variable x.

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Difference Between Assignment Operator (=) and Comparison Operator (==)

Beginners often confuse the assignment operator (=) with the comparison operator (==). Although they look similar, they perform completely different tasks.

Assignment Operator (=)	Comparison Operator (==)
Assigns a value to a variable.	Compares two values.
Used to store data.	Used to check equality.
Does not return True or False.	Returns either True or False.
Example: x = 10	Example: x == 10

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Example 1: Assignment Operator

marks = 95

print(marks)

Output

95

Here, the value 95 is assigned to the variable marks.

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Example 2: Comparison Operator

marks = 95

print(marks == 95)

print(marks == 80)

Output

True

False

The comparison operator checks whether two values are equal and returns a Boolean value (True or False).

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Think Like a Programmer

Predict the output of the following program:

x = 15

print(x == 15)

print(x == 20)

x = 20

print(x)

Answer

True

False

20

The first two statements compare values, while the third statement changes the value stored in the variable.

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Rules for Naming Variables

• Must begin with a letter or underscore (_).
• Cannot begin with a digit.
• Can contain letters, digits, and underscores.
• Cannot contain spaces.
• Cannot use Python keywords.
• Python is case-sensitive.

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Valid Variable Names

Variable Name	Valid?
student	✔ Yes
roll_no	✔ Yes
_salary	✔ Yes
marks2026	✔ Yes

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Invalid Variable Names

Variable Name	Reason
2marks	Starts with a digit
student name	Contains a space
class	Python keyword
total-marks	Contains hyphen (-)

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Python is Case-Sensitive

Python treats uppercase and lowercase letters as different.

name = "Riya"

Name = "Aman"

print(name)

print(Name)

Output

Riya

Aman

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Dynamic Typing

Python is a dynamically typed language. The data type of a variable is determined automatically based on the value assigned to it.

x = 25

x = "Python"

x = 45.6

The same variable x stores an integer, then a string, and finally a floating-point value.

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Multiple Assignment

Python allows multiple variables to be assigned values in a single statement.

Example 1

a = b = c = 100

All three variables store the value 100.

Example 2

x, y, z = 10, 20, 30

Variable	Value
x	10
y	20
z	30

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Swapping Variables

Python provides a simple way to exchange the values of two variables without using a third variable.

a = 10

b = 20

a, b = b, a

print(a)

print(b)

Output

20

10

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Variable Naming Conventions

Although Python allows many styles of naming variables, following standard naming conventions improves code readability.

Convention	Example
Use meaningful names	student_name
Use lowercase letters	total_marks
Separate words using underscore	annual_salary
Avoid single-letter names (except loop variables)	student_age

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Think Like a Programmer

Predict the value stored in each variable after executing the following code:

x = 10

y = x

x = 20

Variable	Final Value
x	20
y	10

Changing x after assigning its value to y does not affect y.

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Real-Life Example

Imagine a student locker.

• The locker number is the variable name.
• The books kept inside the locker are the variable value.
• The books can be replaced, but the locker number remains the same.

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Common Errors

• Using keywords as variable names.
• Starting variable names with digits.
• Using spaces in variable names.
• Confusing = with ==.
• Ignoring Python's case sensitivity.

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Exam Tips

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Frequently Asked Questions (FAQs)

1. What is a variable?

A variable is a named memory location used to store data.

2. Does Python require variable declaration?

No. Variables are created automatically when values are assigned.

3. Is Python case-sensitive?

Yes. Variables such as name and Name are different.

4. What is dynamic typing?

Dynamic typing means the data type of a variable is determined automatically during execution.

5. Can multiple variables be assigned in one statement?

Yes. Python supports multiple assignment.

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Summary

• Variables store data in memory.
• Variables are created automatically during assignment.
• Variable names must follow Python naming rules.
• Python is a dynamically typed language.
• Multiple assignment and variable swapping are simple in Python.
• Meaningful variable names improve program readability and maintenance.