Unit 4: Modules and Packages & File Handling

Modules and Packages in Python

A module is a file that contains Python code such as functions, variables, and classes, which can be reused in other programs.

Advantages of Modules

• Code reusability
• Easy maintenance
• Better organization
• Faster development

User-Defined Modules

A module created by the user.

Steps to Create and Use a Module

Step 1: Create a module

# mymodule.py
def add(a, b):
    return a + b

Step 2: Import module

import mymodule
print(mymodule.add(10, 20))

Ways to Import a Module

Import Style	Example
import module	import math
from module import name	from math import sqrt
alias	import math as m

What is a Package?

A package is a collection of related modules stored in directories.

mypackage/
 ├── module1.py
 ├── module2.py
 └── __init__.py

Standard Library Modules

Python provides a rich standard library to perform common tasks.

random Module

Used to generate random numbers.

Function	Use
random()	Float between 0–1
randint(a,b)	Integer between a and b
choice()	Random element

import random
print(random.randint(1, 10))

NumPy Module

Used for numerical and array operations (scientific computing).

Feature	Description
ndarray	Multi-dimensional array
Fast	Faster than lists
Math Ops	Vector operations

import numpy as np
arr = np.array([1,2,3])
print(arr * 2)

SciPy Module

Built on NumPy, used for advanced scientific calculations.

Applications

• Optimization
• Statistics
• Linear Algebra
• Signal Processing

from scipy import constants
print(constants.pi)

sys Module

Used to interact with Python interpreter & system.

Function	Purpose
sys.argv	Command-line args
sys.exit()	Exit program
sys.path	Module search path

import sys
print(sys.version)

Math Module

Used for mathematical operations.

Function	Meaning
sqrt()	Square root
pow()	Power
ceil()	Round up
floor()	Round down
factorial()	Factorial

import math
print(math.sqrt(16))

String Module

Provides string constants & utilities.

Constant	Meaning
ascii_letters	a–z, A–Z
digits	0–9
punctuation	Special symbols

import string
print(string.digits)

List (Built-in List Functions)

Function	Use
len()	Length
max()	Maximum
min()	Minimum
sum()	Sum
sorted()	Sort

lst = [3,1,2]
print(sorted(lst))

Date & Time Module (datetime)

Used to handle date and time.

Class	Use
datetime	Date & time
date	Date only
time	Time only

from datetime import datetime
now = datetime.now()
print(now)

Regular Expressions (re Module)

Used for pattern matching in strings.

import re

match()

Checks pattern only at beginning.

import re
text = "Python is easy"
print(re.match("Python", text))

search()

Searches pattern anywhere in string.

print(re.search("easy", text))

replace() (sub method)

Replaces matched pattern.

print(re.sub("easy", "powerful", text))

Regex Comparison Table

Function	Behavior
match()	Beginning only
search()	Anywhere
sub()	Replace text

Important Exam Points

• Module = single file
• Package = collection of modules
• NumPy & SciPy used for scientific computing
• sys interacts with interpreter
• math handles calculations
• Regex used for pattern matching

Frequently Asked Exam Questions

• Define module and package
• Difference between NumPy and SciPy
• Explain random and math module
• What is regex? Explain match & search
• Write short note on sys module

File Handling in Python

File handling means storing data permanently in files and reading/writing data from them.

Why File Handling is Needed

• Data persistence (data is not lost after program ends)
• Handling large data
• Data sharing between programs

File Types in Python

Main Types of Files

File Type	Description	Example
Text File	Human readable	.txt, .csv
Binary File	Machine readable	.bin, .dat, .jpg

Creating a File

A file is created using open() function with write mode.

Syntax: file = open("data.txt", "w")

⚠ If file already exists, it is overwritten.

Opening a File

Syntax: file = open("filename", "mode")

Common Modes

• r → read
• w → write
• a → append

file = open("data.txt", "r")

Closing a File

Always close file to free memory.

Syntax: file.close()

Writing Data to File

file = open("data.txt", "w")
file.write("Welcome to Python")
file.close()

Reading Data from File

Read Methods

Method	Use
read()	Read entire file
readline()	Read one line
readlines()	Read all lines

file = open("data.txt", "r")
print(file.read())
file.close()

Renaming a File

Using os module.

import os
os.rename("data.txt", "newdata.txt")

Deleting a File

import os
os.remove("newdata.txt")

Accessing File Properties

Function	Description
file.name	File name
file.mode	File mode
file.closed	File status

print(file.name)

File Pointer (File Cursor)

A file pointer indicates current position in the file.

Methods

Method	Use
tell()	Current position
seek()	Change position

file = open("data.txt", "r")
print(file.tell())
file.seek(0)

File Modes (Detailed Table)

Mode	Meaning
r	Read only
w	Write (overwrite)
a	Append
r+	Read & write
w+	Write & read
a+	Append & read
rb	Read binary
wb	Write binary

Binary Files

Binary files store data in 0s and 1s.

Example: Writing Binary File

file = open("data.bin", "wb")
file.write(b"Hello")
file.close()

Example: Reading Binary File

file = open("data.bin", "rb")
print(file.read())
file.close()

with Statement (Best Practice)

Automatically closes file.

with open("data.txt", "r") as file:
    print(file.read())

Text vs Binary File (Exam Table)

Feature	Text File	Binary File
Readable	Yes	No
Storage	Characters	Bytes
Mode	r, w	rb, wb

Important Exam Points

• File handling provides permanent storage
• Always close file after use
• File pointer tracks read/write position
• Binary files use rb and wb modes
• with statement is safest

Frequently Asked Exam Questions

• Explain file handling with example
• Difference between text and binary files
• Explain file modes
• What is file pointer?
• Write program to read and write file