Monday, June 8, 2026

Introduction

Python provides reusable code using modules, packages, and libraries. These help programmers write organized, reusable, and efficient programs.

Easy Memory Trick

Term	Meaning	Example
Module	Single Python file	math.py
Package	Folder containing modules	numpy.random
Library	Collection of packages and modules	NumPy, Pandas

Easy Analogy

Library = House
Package = Room
Module = Book

A house contains rooms, and rooms contain books.

Similarly:

Library → Packages → Modules

MODULE

Definition

A module is a single Python file (.py) containing reusable code such as functions, classes, variables, and statements.

Modules help reduce repetition and make programs organized.

Types of Modules

1. Built-in Module

A built-in module is a module already provided by Python that contains predefined functions, classes, and variables to perform specific tasks.

These modules are available automatically after Python installation.

Examples

· math

· random

· os

· sys

· datetime

Example Program

import math

print(math.sqrt(25))

Output

5.0

2. User-defined Module

A user-defined module is a module created by the programmer to store reusable code such as functions, classes, and variables in a separate Python file.

Example

# calculator.py

def add(a, b):

    return a + b

Using the Module

import calculator

print(calculator.add(5, 3))

Output

Advantages of Modules

1. Reuse code multiple times

2. Reduce code duplication

3. Make programs organized

4. Simplify testing and debugging

5. Improve readability

Methods of Importing Modules

1. Import Entire Module

import math

Example

print(math.factorial(5))

Output

2. Import Specific Function

from math import sqrt

Example

print(sqrt(49))

Output

7.0

3. Import Module Using Alias

An alias is an alternative short name given to a module during import using the as keyword.

Example

import math as m

print(m.sqrt(64))

Output

8.0

4. Import all functions from a module

Importing all functions from a module means importing every function, variable, and object from a module into the current program using the * symbol.

from module_name import *

Example:

from math import *

print(sqrt(25))

print(factorial(5))

Output

5.0

Important Point

After importing with *, functions can be used directly without writing the module name.

Example:

sqrt(25)

Instead of:

math.sqrt(25)

PACKAGE

Definition

A package is a collection of related Python modules organized inside a folder or directory.

Packages help organize large Python projects systematically.

Structure of a Package

calculator/

│

├── add.py

├── subtract.py

└── __init__.py

init.py File

__init__.py is a special file used to indicate that a directory should be treated as a Python package.

Advantages of Packages

1. Groups related modules together

2. Organizes large projects

3. Improves code management

4. Avoids naming conflicts

5. Supports hierarchical structure

Example of Package Import

from calculator.add import add

Important Points About Packages

· Contains one or more modules

· Usually includes __init__.py

· Can contain sub-packages

· Provides hierarchical organization

LIBRARY

Definition

A library is a collection of modules and packages that provides reusable functionality for specific tasks.

Libraries help programmers perform complex tasks easily and quickly.

Types of Libraries

1. Standard Library

A standard library is a collection of built-in modules that are automatically available with Python installation.

Examples

· math

· random

· os

· datetime

2. External Library

An external library is a library that is not included with Python by default and must be installed separately using pip.

Examples

· NumPy

· Pandas

· Matplotlib

· TensorFlow

· OpenCV

· Django

Popular Python Libraries

Library	Main Use
NumPy	Numerical Computing
Pandas	Data Analysis
Matplotlib	Data Visualization
Requests	API Calls
TensorFlow	Machine Learning
OpenCV	Computer Vision
Django	Web Development

pip

Definition

pip is Python’s package manager used to install, update, and remove external packages and libraries.

Common pip Commands

Install Package

pip install numpy

Uninstall Package

pip uninstall numpy

Show Installed Packages

pip list

Check pip Version

pip --version

Advantages of pip

1. Installs external libraries easily

2. Updates packages

3. Removes unwanted packages

4. Manages dependencies

5. Simplifies package management

📊 Difference Between Module, Package and Library

Feature	Module	Package	Library
Meaning	Single Python file	Collection of modules	Collection of packages and modules
Size	Smallest	Medium	Largest
Form	`.py` file	Folder/Directory	Complete collection
Purpose	Reuse code	Organize modules	Provide complete functionality
Example	math.py	numpy.random	NumPy

Common Exam Mistakes

❌ Confusing module and package
❌ Writing package as a single file
❌ Forgetting .py extension in module definition
❌ Writing pip as a library instead of package manager

Final Summary

A module is a single Python file containing reusable code. A package is a collection of related modules stored inside a folder. A library is a collection of modules and packages that provides reusable functionality for developers.

4.2 USER-DEFINED FUNCTIONS IN PYTHON

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4.2 USER-DEFINED FUNCTIONS IN PYTHON

What is a Function?

A function is a block of organized and reusable code designed to perform a specific task.

Functions help reduce repetition and make programs easier to manage.

Advantages of Functions

v Reuse code multiple times.

v Reduce code duplication.

v Improve program readability.

v Make debugging easier.

v Support modular programming.

Modularity

Modularity means dividing a large program into smaller and manageable parts called functions or modules.

Types of Functions in Python

There are two types of functions:

v Built-in Functions

v User-defined Functions

1. Built-in Functions (Library Functions)

Functions already provided by Python are called built-in functions.

These functions are automatically available.

Common Built-in Functions

Function	Purpose	Examples
print( )	Displays output	print("Hello")
input( )	Takes input
len( )	Returns length	len("Python")
int( )	Converts into integer	int("5")
sum( )	Calculates total	sum([1,2,3])

2. User-defined Functions

A function created by the programmer using the def keyword is called a user-defined function.

Example

def greet( ):
print("Hello")

Difference Between Built-in and User-defined Functions

Feature	Built-in Function	User-defined Function
Creator	Python Developers	Programmer
Availability	Available by default	Must be created
Loading	Loaded automatically	Loaded when defined
Example	print( )	add( )

Creating a User-defined Function

Syntax

def function_name(parameters):
statements
return value

Example Program

def add_numbers(x, y):
total = x + y
return total

print(add_numbers(5, 6))

Output

Important Rules of Functions

v Function definition starts with def

v Function header ends with colon :

v Indentation is compulsory

v Function name should be meaningful

v Parameters are optional

v Return statement is optional

Return Statement

A statement used to send a value back from a function.

Syntax

return value

Function Returning Value

Example

def area(length, width):
return length * width

result = area(5, 8)

print(result)

Output

Parameters and Arguments

Parameter

A variable written inside the function definition is called a parameter.

Example

def area(radius):

radius is a parameter.

Argument

The actual value passed during the function call is called an argument.

Example

area(5)

5 is an argument.

Difference Between Parameter and Argument

Parameter	Argument
Placeholder	Actual value
Used in definition	Used in function call
Variable	Value

Example

def add(x, y):
return x + y

add(5, 3)

Item	Type
x, y	Parameters
5, 3	Arguments

Scope of Variables

Scope determines where a variable can be accessed.

Types of Scope

v Local Scope

v Global Scope

Local Scope

Variables declared inside a function and accessible only within that function.

Example

def test():
num = 5
print(num)

test( )

Global Scope

Variables declared outside functions and accessible throughout the program.

Example

num = 10

def show( ):
print(num)

show( )

Passing Arguments

Python supports three types of arguments.

v Positional Arguments

v Default Arguments

v Keyword Arguments

1. Positional Arguments

Arguments are passed in the same order as parameters.

Example

def check(a, b, c):
print(a, b, c)

check(2, 5, 7)

Output

2 5 7

2. Default Arguments

Parameters are assigned default values.

Example

def power(base, exp=2):
return base ** exp

print(power(4))
print(power(2,3))

Output

16
8

Important Rule for Default Arguments

✅ Required parameters first
✅ Default parameters last

Legal Function

def interest(prin, time, rate=0.10):

Illegal Function

def interest(prin, time=2, rate):

❌ Error occurs because default arguments must come after required arguments.

3. Keyword Arguments

Arguments are passed using parameter names.

Order does not matter.

Example

def interest(prin, time, rate):
pass

interest(rate=0.10, prin=2000, time=2)

Types of Functions Based on Return Value

v Void Function

v Non-Void Function

Void Function

A function that does not return any value.

Non-Void Function

A function that returns a value.

Example

def add(x, y):
return x + y

result = add(5,3)

Returning Multiple Values

Python can return multiple values using one return statement.

Example

def squared(x, y, z):
return x*x, y*y, z*z

print(squared(2,5,7))

Output

(4, 25, 49)

Example with Variables

def squared(x, y, z):
return x*x, y*y, z*z

a, b, c = squared(2,3,4)

print(a, b, c)

Output

4 9 16

Common Exam Mistakes ❌

v Forgetting colon : after function definition

v Wrong indentation

v Confusing parameter and argument

v Writing default arguments before required arguments

v Forgetting to call the function

Most Important Programs for SEE Exam