Introduces key libraries · Kalviyogi Smart Notes OS

Definition

Meaning

A Python Library என்பது particular tasks செய்ய தேவையான pre-written code, functions, classes, modules ஆகியவற்றின் collection.

Simple definition

நாமே எல்லா code-ஐயும் scratch-லிருந்து எழுதாமல், already created functions-ஐ பயன்படுத்த உதவுவது Python Library.

Program

Example

Python 1 lines

1import math

import math

Program

Python 1 lines

1print(math.sqrt(25))

print(math.sqrt(25))

Verified output

5.0

Learning Run Mode — this is the output the author verified, not a live execution.

Output

5.0

இங்கு square root calculate செய்ய algorithm நாமே எழுதவில்லை.

Python-ன் math module-ல் already இருக்கும்:

sqrt()

function-ஐ பயன்படுத்துகிறோம்.

Simple Explanation

Core idea

ஒரு carpenter-க்கு toolbox இருக்கும்.

Toolbox-ல்

Hammer
Screwdriver
Spanner
Cutter

Detail 02

எல்லாம் ready-made tools.

Detail 03

அதே மாதிரி Python programmer-க்கு libraries/modules இருக்கும்.

For example

math → Mathematical functions

Detail 05

random → Random values

Detail 06

statistics → Statistical calculations

Detail 07

datetime → Date and time

Detail 08

os → Operating system related operations

Detail 09

sys → Python/system related information

Detail 10

json → JSON data

Detail 11

csv → CSV files

Detail 12

re → Regular expressions

Detail 13

NumPy → Numerical computing

Detail 14

Pandas → Data analysis

Detail 15

Matplotlib → Graphs and charts

Flow

Problem / Task
Required library identify செய்கிறோம்
Library import செய்கிறோம்
Required function call செய்கிறோம்
Python executes library code
Result கிடைக்கும்

Program

Example

Python 9 lines

1Need square root
2↓
3Use math
4↓
5import math
6↓
7math.sqrt(25)
8↓
95.0

Need square root
↓
Use math
↓
import math
↓
math.sqrt(25)
↓
5.0

Syntax

Python 2 lines

1Basic Import
2import library_name

Basic Import
import library_name

Program

Example

Python 3 lines

1import math
2Using a Function
3library_name.function_name()

import math
Using a Function
library_name.function_name()

Program

Example

Python 3 lines

1math.sqrt(25)
2Import Specific Function
3from library_name import function_name

math.sqrt(25)
Import Specific Function
from library_name import function_name

Program

Example

Python 1 lines

1from math import sqrt

from math import sqrt

Program

Python 3 lines

1print(sqrt(25))
2Import with Alias
3import library_name as alias

print(sqrt(25))
Import with Alias
import library_name as alias

Program

Example

Python 1 lines

1import numpy as np

import numpy as np

Explanation

Core idea

np → Alias

Here

numpy → Original library name

Program

Program 1

Python 2 lines

1Using math
2import math

Using math
import math

Program

Python 1 lines

1x = 25

x = 25

Program

Python 1 lines

1result = math.sqrt(x)

result = math.sqrt(x)

Program

Python 1 lines

1print(result)

print(result)

Verified output

5.0

Learning Run Mode — this is the output the author verified, not a live execution.

Output

5.0

Line by Line

1

import math

Python-ன் math module-ஐ program-க்கு available ஆக்குகிறது.

2

x = 25

x variable-க்கு 25 assign செய்கிறோம்.

3

result = math.sqrt(x)

math.sqrt() square root calculate செய்யும் function. So: √25 = 5 Python result: 5.0

4

print(result)

Calculated result screen-ல் display ஆகிறது.

Dry Run

Execution traceRead top to bottom · highlighted cells show the current value4 states

Step	Statement	x	result	Output
01Iteration 1	import math	-	-	-
02Iteration 2	x = 25	25	-	-
03Iteration 3	math.sqrt(x)	25	5.0	-
04Iteration 4	print(result)	25	5.0	5.0

Definition

Meaning

A module என்பது Python code இருக்கும் ஒரு file.

ஒரு module-ல்

Functions
Variables
Classes
Constants
இருக்கலாம்.

Program

Example

Python 1 lines

1import math

import math

Explanation

Core idea

math ஒரு module.

Simple Explanation

Core idea

Python-லும் different modules different வேலைகளுக்காக இருக்கும்.

ஒரு notebook-ல் ஒரு particular subject notes இருப்பது போல

Math notebook
Science notebook
English notebook

Comparison

Term	Simple Meaning
Module	ஒரு Python code unit/file
Package	பல related modules-ன் collection
Library	reusable code collection என்ற broad term

Comparison

Simple memory:	Module
↓	Small unit
Package	↓
Collection of modules	Library
↓	Ready-made functionality

Important

Students basic level-ல் math library, random library என்று சொல்லலாம்.
Technically
math, random, statistics போன்றவை Python Standard Library-ல் உள்ள modules.

Definition

Meaning

Python install செய்தவுடன் available ஆகும் large collection of modules-ஐ Python Standard Library என்று கூறுகிறோம்.

பல modules-க்கு separate installation தேவையில்லை.

Examples

math
random
statistics
datetime
os
sys
json
csv
re

Memory Trick

Standard Library = Python உடன் வரும் ready-made tools

Definition

Meaning

math module mathematical calculations செய்ய useful.

Import

import math

Table

Common math functions

Function	Purpose
math.sqrt()	Square root
math.pow()	Power
math.ceil()	Round upward
math.floor()	Round downward
math.factorial()	Factorial
math.sin()	Sine
math.cos()	Cosine
math.log()	Logarithm

Important

Important constants
math.pi
math.e

Program

Python 2 lines

1Square Root
2import math

Square Root
import math

Program

Python 1 lines

1print(math.sqrt(64))

print(math.sqrt(64))

Verified output

8.0

Learning Run Mode — this is the output the author verified, not a live execution.

Output

8.0

Program

Python 2 lines

1Power
2import math

Power
import math

Program

Python 1 lines

1print(math.pow(2, 3))

print(math.pow(2, 3))

Verified output

8.0

Learning Run Mode — this is the output the author verified, not a live execution.

Output

8.0

Program

Python 2 lines

1Pi
2import math

Pi
import math

Program

Python 1 lines

1print(math.pi)

print(math.pi)

Explanation

Output approximately

3.141592653589793

Program

Python 2 lines

1Ceiling and Floor
2import math

Ceiling and Floor
import math

Program

Python 1 lines

1x = 4.7

x = 4.7

Program

Python 2 lines

1print(math.ceil(x))
2print(math.floor(x))

print(math.ceil(x))
print(math.floor(x))

Verified output

5
4

Learning Run Mode — this is the output the author verified, not a live execution.

Output

5
4

Explanation

math.ceil(4.7)

means

4.7-க்கு next higher integer

5

math.floor(4.7)

4.7-க்கு lower integer

4

Program

Python 2 lines

1Factorial
2import math

Factorial
import math

Program

Python 1 lines

1print(math.factorial(5))

print(math.factorial(5))

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Because:

5! = 5 × 4 × 3 × 2 × 1
= 120

Definition

Meaning

random module pseudo-random values generate செய்ய பயன்படுகிறது.

Import

import random

Simple Explanation

Core idea

Dice throw பண்ணினால் எந்த number வரும் என்று முன்னதாக exact-ஆ தெரியாது.

அதே மாதிரி random number generate செய்ய

random

Detail 02

module use செய்யலாம்.

Program

Python 2 lines

1Random Integer
2import random

Random Integer
import random

Program

Python 1 lines

1x = random.randint(1, 6)

x = random.randint(1, 6)

Program

Python 1 lines

1print(x)

print(x)

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Possible output

அடுத்த execution

2

அல்லது

6

வரலாம்.

Important

random.randint(1, 6)
means
1 முதல் 6 வரை inclusive random integer.
Both
1
and
6
can occur.

Program

Python 2 lines

1Random Choice
2import random

Random Choice
import random

Explanation

Core idea

names = ["Arun", "Bala", "Kumar"]

Program

Python 1 lines

1print(random.choice(names))

print(random.choice(names))

Verified output

Bala

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Possible output

Bala

Table

Common random functions

Function	Purpose
random.random()	Random float from 0.0 up to, but not including, 1.0
random.randint(a,b)	Random integer from a to b inclusive
random.choice()	Choose one item
random.shuffle()	Shuffle items

Common Mistake

random.randint(1, 5) means only 1 to 4 என்று நினைக்க வேண்டாம்.

Correct:

1, 2, 3, 4, 5

all possible.

Definition

Meaning

statistics module basic statistical calculations செய்ய பயன்படுகிறது.

Example calculations

Mean
Median
Mode

Import

import statistics

Program

Python 1 lines

1import statistics

import statistics

Explanation

Core idea

marks = [80, 90, 70, 100]

Program

Python 1 lines

1print(statistics.mean(marks))

print(statistics.mean(marks))

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Explanation

Values

80 + 90 + 70 + 100 = 340

Number of values

4

Mean

340 / 4 = 85

Program

Python 2 lines

1Median
2import statistics

Median
import statistics

Explanation

Core idea

data = [10, 20, 30, 40, 50]

Program

Python 1 lines

1print(statistics.median(data))

print(statistics.median(data))

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Program

Python 2 lines

1Mode
2import statistics

Mode
import statistics

Explanation

Core idea

data = [10, 20, 20, 30]

Program

Python 1 lines

1print(statistics.mode(data))

print(statistics.mode(data))

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Because 20 occurs most frequently.

Definition

Meaning

datetime module date and time operations செய்ய பயன்படுகிறது.

Program

Python 1 lines

1import datetime

import datetime

Program

Python 1 lines

1today = datetime.date.today()

today = datetime.date.today()

Program

Python 1 lines

1print(today)

print(today)

Explanation

Output will be the current system date in a form such as

2026-08-11

Important

datetime useful for
Current date
Current time
Date difference
Age calculations
Scheduling applications
Logging

Definition

Meaning

os module operating system related functionality access செய்ய பயன்படுகிறது.

Import

import os

Program

Python 2 lines

1Current Working Directory
2import os

Current Working Directory
import os

Program

Python 1 lines

1print(os.getcwd())

print(os.getcwd())

Verified output

C:\Users\Admin\Documents

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Possible output

C:\Users\Admin\Documents

Important

os module can help with
Files
Folders
Paths
Environment variables
Current working directory

Definition

Meaning

sys module Python interpreter மற்றும் runtime environment related information/functionality access செய்ய பயன்படுகிறது.

Program

Python 1 lines

1import sys

import sys

Program

Python 1 lines

1print(sys.version)

print(sys.version)

Verified output

3.x.x ...

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Possible output

3.x.x ...

Important

Common
sys.version
→ Python version information
sys.argv
→ Command-line arguments
sys.exit()
→ Program exit

Definition

Meaning

json module JSON data-ஐ Python data-ஆக convert செய்யவும், Python data-ஐ JSON format-ஆக convert செய்யவும் பயன்படுகிறது.

JSON is very common in

Web applications
APIs
Mobile apps
Data exchange

Program

Python 1 lines

1import json

import json

Program

Python 4 lines

1student = {
2    "name": "Arun",
3    "mark": 90
4}

student = {
    "name": "Arun",
    "mark": 90
}

Program

Python 1 lines

1result = json.dumps(student)

result = json.dumps(student)

Program

Python 1 lines

1print(result)

print(result)

Verified output

{"name": "Arun", "mark": 90}

Learning Run Mode — this is the output the author verified, not a live execution.

Output

{"name": "Arun", "mark": 90}

Definition

Meaning

csv module CSV files read/write செய்ய பயன்படுகிறது.

CSV

Comma-Separated Values

Explanation

Example

Core idea

Name,Mark
Arun,90
Bala,85

CSV commonly used for

Student data
Reports
Excel-compatible data exchange
Datasets

Definition

re means

Regular Expression

Text pattern search மற்றும் matching செய்ய பயன்படுகிறது.

Program

Python 1 lines

1import re

import re

Explanation

Core idea

text = "My number is 12345"

Program

Python 1 lines

1result = re.findall(r"\d+", text)

result = re.findall(r"\d+", text)

Program

Python 1 lines

1print(result)

print(result)

Verified output

['12345']

Learning Run Mode — this is the output the author verified, not a live execution.

Output

['12345']

Simple Explanation

re useful for

Phone number validation
Email pattern validation
Search
Text processing
Data cleaning

Third-Party Libraries

Context

Python-உடன் default installation-ல் எல்லா external libraries-மும் வராது.

Some libraries separately install செய்ய வேண்டும்.

Common examples

NumPy
Pandas
Matplotlib
SciPy
Requests

Explanation

Core idea

pip install numpy

Installation generally

pip install library_name

Detail 02

Then:

Program

Python 1 lines

1import numpy

import numpy

Definition

Meaning

NumPy என்பது numerical computing மற்றும் arrays-க்கு widely used Python library.

NumPy

Numerical Python

Common alias

import numpy as np

Program

Python 1 lines

1import numpy as np

import numpy as np

Program

Python 1 lines

1numbers = np.array([10, 20, 30])

numbers = np.array([10, 20, 30])

Program

Python 1 lines

1print(numbers)

print(numbers)

Verified output

[10 20 30]

Learning Run Mode — this is the output the author verified, not a live execution.

Output

[10 20 30]

Important

NumPy useful for
Arrays
Matrix operations
Mathematical calculations
Scientific computing
Machine learning foundations

Definition

Meaning

Pandas என்பது structured/table data analysis மற்றும் manipulation செய்ய பயன்படும் popular Python library.

Common alias

import pandas as pd

Program

Python 1 lines

1import pandas as pd

import pandas as pd

Program

Python 4 lines

1data = {
2    "Name": ["Arun", "Bala"],
3    "Mark": [90, 85]
4}

data = {
    "Name": ["Arun", "Bala"],
    "Mark": [90, 85]
}

Program

Python 1 lines

1df = pd.DataFrame(data)

df = pd.DataFrame(data)

Program

Python 1 lines

1print(df)

print(df)

Verified output

Name  Mark
0  Arun    90
1  Bala    85

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Possible output

Name  Mark
0  Arun    90
1  Bala    85

Important

Pandas main structures
Series
DataFrame

Definition

Meaning

Matplotlib என்பது graphs, plots மற்றும் charts உருவாக்க பயன்படும் visualization library.

Common import

import matplotlib.pyplot as plt

Program

Python 1 lines

1import matplotlib.pyplot as plt

import matplotlib.pyplot as plt

Explanation

Core idea

x = [1, 2, 3]
y = [10, 20, 30]

Detail 01

plt.plot(x, y)
plt.show()

Detail 02

This displays a line graph.

Important

Matplotlib useful for
Line graph
Bar chart
Pie chart
Scatter plot
Data visualization

Comparison

Important Libraries at a Glance

Library / Module	Main Purpose
math	Mathematical functions
random	Random values
statistics	Mean, median, mode
datetime	Date and time
os	Operating system tasks
sys	Python/system information
json	JSON processing
csv	CSV files
re	Pattern matching
NumPy	Arrays and numerical computing
Pandas	Data analysis
Matplotlib	Graphs and charts

Comparison

Standard Library vs Third-Party Library

Point	Standard Library	Third-Party Library
Availability	Comes with Python distribution	Usually installed separately
Installation	Usually no extra pip installation	Often pip install required
Example	math	NumPy
Example	random	Pandas
Example	datetime	Matplotlib

Important

import Statement
To use a module
import math
Then
math.sqrt(25)
Notice
module.function()

Different Ways of Importing

Program

Python 2 lines

1Method 1
2import math

Method 1
import math

Program

Python 3 lines

1print(math.sqrt(25))
2Method 2
3from math import sqrt

print(math.sqrt(25))
Method 2
from math import sqrt

Program

Python 1 lines

1print(sqrt(25))

print(sqrt(25))

Here math. prefix தேவையில்லை.

Program

Python 2 lines

1Method 3 - Alias
2import math as m

Method 3 - Alias
import math as m

Program

Python 1 lines

1print(m.sqrt(25))

print(m.sqrt(25))

Verified output

NameError

Learning Run Mode — this is the output the author verified, not a live execution.

m என்பது alias.

Comparison

Method	Example	Function Call
Normal import	import math	math.sqrt(25)
Specific import	from math import sqrt	sqrt(25)
Alias	import math as m	m.sqrt(25)

Common Mistake

Error 1

Context

Library import செய்யாமல் function call செய்வது

Wrong

print(math.sqrt(25))

without

import math

Output

Possible result

NameError

Program

Correct

Python 1 lines

1import math

import math

Program

Python 1 lines

1print(math.sqrt(25))

print(math.sqrt(25))

Common Mistake

Error 2

Context

Wrong Function Name

Wrong

math.squareroot(25)

Correct

math.sqrt(25)

Common Mistake

Error 3

Context

Case mistake

Python is case-sensitive.

Wrong

Math.sqrt(25)

Correct

math.sqrt(25)

Common Mistake

Error 4

Alias பயன்படுத்திய பிறகு original alias form confuse செய்வது
import numpy as np

Then normally:

np.array([1, 2, 3])

Use the imported name np.

Common Mistake

Error 5

Module and Function confuse செய்வது
import math

math → module

math.sqrt()

sqrt → function

Remember

M R S D O S J C R
M → Math
R → Random
S → Statistics
D → Datetime
O → OS
S → Sys
J → JSON
C → CSV
R → Regular Expression
For Data Science
N P M
N → NumPy
P → Pandas
M → Matplotlib

TRB Point

TRB Point 1

A library provides reusable code for common programming tasks.

TRB Point

TRB Point 2

Python uses the import statement to access modules.

TRB Point

TRB Point 3

math provides mathematical functions.

TRB Point

TRB Point 4

math.sqrt()
calculates square root.

TRB Point

TRB Point 5

math.factorial()
calculates factorial.

TRB Point

TRB Point 6

random is used for pseudo-random values.

TRB Point

TRB Point 7

random.randint(a, b)
returns a random integer between a and b, inclusive.

TRB Point

TRB Point 8

statistics.mean() calculates arithmetic mean.

TRB Point

TRB Point 9

datetime handles dates and times.

TRB Point

TRB Point 10

os provides operating-system-related functionality.

TRB Point

TRB Point 11

sys.version provides Python version information.

TRB Point

TRB Point 12

json is used for JSON encoding and decoding.

TRB Point

TRB Point 13

csv supports CSV file processing.

TRB Point

TRB Point 14

re supports regular expressions.

TRB Point

TRB Point 15

NumPy is mainly associated with numerical arrays and scientific computing.

TRB Point

TRB Point 16

Pandas is widely used for data analysis.

TRB Point

TRB Point 17

Matplotlib is widely used for plotting and data visualization.

Interview Point

Question 1

What is a Python library?

Answer

A Python library is a collection of reusable code that provides functions, classes, and modules for performing particular tasks without writing everything from scratch.

Interview Point

Question 2

What is the Python Standard Library?

Answer

The Python Standard Library is a collection of modules distributed with Python that provide functionality such as mathematics, file handling, dates, JSON processing, and operating-system interaction.

Interview Point

Question 3

What is the purpose of import?

Answer

The import statement makes a module or its contents available for use in the current program.

Interview Point

Question 4

What is the difference between math and NumPy?

Answer

math mainly provides mathematical functions for ordinary numeric values. NumPy provides powerful multidimensional arrays and vectorized numerical operations for scientific and data-oriented computing.

Interview Point

Question 5

Why do we use aliases?

Answer

Aliases provide shorter or conventional names for modules.

Program

Example

Python 1 lines

1import numpy as np

import numpy as np

Verified output

12.0

Learning Run Mode — this is the output the author verified, not a live execution.

MCQ

193Which keyword is used to load a Python module?

Choose one answer

MCQ

194Which module provides mathematical functions?

Choose one answer

MCQ

195What is the output? import math print(math.sqrt(81))

Choose one answer

MCQ

196Which function calculates factorial?

Choose one answer

MCQ

197Which module can generate random numbers?

Choose one answer

MCQ

198What values may this generate? random.randint(1, 3)

Choose one answer

MCQ

199Which module contains mean()?

Choose one answer

MCQ

200Which module is mainly used with dates and times?

Choose one answer

MCQ

201What does os.getcwd() commonly return?

Choose one answer

MCQ

202Which expression gives Python version information?

Choose one answer

MCQ

203JSON processing is mainly provided by:

Choose one answer

MCQ

204CSV stands for:

Choose one answer

MCQ

205Which library is widely used for arrays?

Choose one answer

MCQ

206The conventional alias for NumPy is:

Choose one answer

MCQ

207Which library is widely used for tabular data analysis?

Choose one answer

MCQ

208Which library is commonly imported as: import matplotlib.pyplot as plt

Choose one answer

MCQ

209What is sqrt in this statement? math.sqrt(25)

Choose one answer

MCQ

210What is math here? import math

Choose one answer

Practice

Practice 1

Use math to find:

√144

Answer:

import math

print(math.sqrt(144))

Output

12.0

Practice

Practice 2

Find:

6!

Program

Python 1 lines

1import math

import math

Program

Python 1 lines

1print(math.factorial(6))

print(math.factorial(6))

Verified output

Learning Run Mode — this is the output the author verified, not a live execution.

Output

Expected output

Practice

Practice 3

Generate a random integer between 1 and 10.

import random

print(random.randint(1, 10))

Practice

Practice 4

Calculate mean:

marks = [80, 70, 90, 100]

Use:

import statistics

print(statistics.mean(marks))

Answer:

85

Practice

Practice 5

Print Python version using sys.

import sys

print(sys.version)

Practice

Practice 6

Print current working directory.

import os

print(os.getcwd())

Practice

Practice 7

Create a NumPy array:

[10, 20, 30, 40]

Answer:

import numpy as np

x = np.array([10, 20, 30, 40])

print(x)

Practice

Practice 8

Identify the correct library:

Graph: ?
Table data: ?
Arrays: ?
Random number: ?
Square root: ?

Answers:

Matplotlib
Pandas
NumPy
random
math

Summary

Python libraries/modules providereusable ready-made code.
importis used to access modules.
math provides mathematicalfunctions.
random generates pseudo-randomvalues.
statistics provides statisticalcalculations.
datetimeworks with date and time.
osworks with operating-system-related functionality.
sys provides Python/runtimeinformation.
json processes JSON.
csv processes CSV files.
re provides regular-expressionsupport.
NumPy provides powerful arrays andnumerical computing.
Pandasis widely used for data analysis.
Matplotlibis widely used for visualization.
import library as aliascreates an alias.
Standard Library modules generallycome with Python.
Third-party libraries commonlyrequire separate installation.

Quick Revision

Library → Ready-made reusable code
Module → Python code unit/module
import → Load/use module
math → Mathematics
sqrt() → Square root
factorial() → Factorial
random → Random values
randint() → Random integer
statistics → Mean, median, mode
datetime → Date and time
os → Operating system
sys → Python/system information
json → JSON data
csv → CSV files
re → Regular expressions
NumPy → Numerical arrays
Pandas → Data analysis
Matplotlib → Graphs
np → Common NumPy alias
pd → Common Pandas alias
plt → Common Matplotlib pyplotalias
Easy Memory: Math = Calculate,Random = Generate, Statistics = Analyze, NumPy = Numbers, Pandas = Data, Matplotlib = Graph.

Third-Party Libraries

Different Ways of Importing

Your note