Introduction to Python

1. Introduction to Python

Python is a high-level, interpreted, and general-purpose programming language. It was created by Guido van Rossum and first released in 1991. Its design philosophy emphasizes code readability, making it an ideal first language for students.

2. Key Features of Python

Python stands out because of its simplicity and power. Here are its core features:

Easy to Learn and Read: Python uses a very clear syntax that looks a lot like English. It uses indentation to define blocks of code instead of curly braces.
Interpreted Language: Python code is executed line-by-line by an interpreter. This makes debugging (finding errors) much easier.
Platform Independent (Portable): You can run the same Python code on Windows, macOS, or Linux without making changes.
Case Sensitive: In Python, Variable and variable are treated as two different things.
Large Standard Library: It comes with a vast collection of pre-written code (modules) that you can use to perform complex tasks easily.
Free and Open Source: You can download Python for free from python.org.

3. Executing a “Hello World” Program

The Code:

print("Hello World")

How it works:

print() is a built-in function used to display output.
The text inside the quotes is called a string.

4. Python Execution Modes

There are two primary ways to run your Python code. Understanding the difference is crucial for efficient coding.

A. Interactive Mode

In this mode, you type one line of code at a time at the Python prompt (>>>), and the interpreter executes it immediately after you press Enter.

Best for: Testing small snippets of code or doing quick calculations.
Limitation: The code is not saved. Once you close the window, your work is gone.

B. Script Mode

In script mode, you write your entire program in a text file and save it with a .py extension (e.g., myscript.py). You then run the entire file at once.

Best for: Writing long programs and projects that you want to save and run later.
How to use:
1. Open a script editor (like IDLE, VS Code, or Notepad).
2. Write your code.
3. Save the file as filename.py.
4. Run the file (usually by pressing F5 in IDLE).

Feature	Interactive Mode	Script Mode
Execution	Line-by-line, immediate	All at once
Saving	Cannot save code	Code is saved in a `.py` file
Editing	Hard to edit previous lines	Easy to edit and re-run
Usage	Quick testing	Building applications

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1. Python Character Set

A character set is a set of valid characters that can be used in a programming language.

Python supports the following characters:

(i) Letters

Uppercase letters: A to Z
Lowercase letters: a to z

Example:

name = "Rahul"

(ii) Digits

0 to 9

Example:

age = 16

(iii) Special Symbols

Symbols used in Python programs.

Examples:

+  -  *  /  %  =  <  >  ( ) { } [ ] ; : " ' #

(iv) White Spaces

Spaces, tabs, and new lines are called white spaces.

Example:

x = 10
y = 20

2. Python Tokens

Tokens are the smallest individual units in a Python program.

Types of Python Tokens:

Keywords
Identifiers
Literals
Operators
Punctuators

2.1 Keywords

Keywords are reserved words that have special meaning in Python.

Examples:

if, else, while, for, break, continue, True, False, class

Example Program:

if 10 > 5:
    print("10 is greater")

Important Points

Keywords cannot be used as variable names.
Python keywords are written in lowercase except True, False, and None.

2.2 Identifiers

Identifiers are names given to different part of the program like:

Variables
Functions
Classes
Objects

Example:

marks = 95
student_name = "Aman"

Rules for Naming Identifiers

Must start with a letter or underscore _
Cannot start with a digit
Cannot contain spaces
Cannot use keywords
Case-sensitive

Valid identifiers :

name
_marks
student1

Invalid identifiers:

1name
class
student name

2.3 Literals

Literals are fixed values used in a program.

Types of Literals

(i) Numeric Literals

Numeric literals are fixed numeric values written directly in a Python program. They represent numbers such as integers, decimals, or complex numbers.

Types of Numeric Literals in Python

1. Integer Literals (`int`)

Integer literals are whole numbers without decimal point.

They can be:

Positive
Negative
Zero

Examples:

10
-25
0

Program:

x = 100
print(x)

Output:

2. Floating Point Literals (`float`)

Numbers containing decimal point are called floating point literals.

Examples:

10.5
-3.14
0.0

Program:

pi = 3.14
distance = 1.2e4  # 1.2 * 10^4 = 12000.0
print(pi)           #3.14
print(distance)     #12000.0

Output:

3.14

3. Complex Literals (`complex`)

Complex numbers contain:

Real part
Imaginary part

Imaginary part is written using j.

Format:

a + bj

Examples:

2 + 3j
5j

Program:

x = 2 + 3j
print(x)    #(2+3j)

Output:

(2+3j)

Different Number Systems in Integer Literals

Python allows integers in different number systems.

Type	Prefix	Example
Decimal	No prefix	25
Binary	`0b`	0b1010
Octal	`0o`	0o17
Hexadecimal	`0x`	0x1A

(i) Decimal Literal

Base 10 numbers.

Example:

x = 25
print(x)

(ii) Binary Literal

Base 2 numbers using digits 0 and 1.

Prefix: 0b

Example:

x = 0b1010
print(x)

Output:

(iii) Octal Literal

Base 8 numbers using digits 0 to 7.

Prefix: 0o

Example:

x = 0o17
print(x)

Output:

(iv) Hexadecimal Literal

Base 16 numbers using digits 0–9 and letters A–F.

Prefix: 0x

Example:

x = 0x1A
print(x)

Output:

Important Points

Numeric literals are fixed numbers in a program.
Python supports:
- Integer literals
- Floating point literals
- Complex literals
Integer literals can also be written in binary, octal, and hexadecimal forms.

Quick Revision

Literal	Example
Integer	`25`
Float	`3.14`
Complex	`2+3j`
Binary	`0b1010`
Octal	`0o17`
Hexadecimal	`0x1A`

(ii) String Literals

"Hello"
'Python'

(iii) Boolean Literals

True
False

(iv) Special Literal

None

2.4 Operators

Operators are symbols used to perform operations.

Example:

a + b

2.5 Punctuators

Punctuators are symbols used to organize Python statements.

Examples:

( ) [ ] { } , : ; " '

Example:

print("Hello")

3. Variables

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

Example:

x = 10
name = "Riya"

Here:

x stores integer value 10
name stores string value “Riya”

4. Concept of l-value and r-value

l-value

The variable present on the left side of assignment operator = is called l-value.

r-value

The value or expression present on the right side is called r-value.

Example:

x = 20

Here:

x → l-value
20 → r-value

Another Example:

a = b + c

a → l-value
b + c → r-value

5. Comments in Python

Comments are notes written in a program to explain the code.

Python ignores comments during execution.

Types of Comments

(i) Single-line Comment

Starts with #

Example:

# This is a comment
print("Hello")

(ii) Multi-line Comment

Written using triple quotes.

Example:

"""
This is
multi-line comment
"""

6. Uses of Comments

Comments are used to:

Explain code
Improve readability
Make debugging easier
Help other programmers understand the program

Example:

# Calculating area of circle
radius = 7
area = 3.14 * radius * radius

7. print() Function

The print() function is used to display output on the screen.

Syntax

print(object(s), sep=separator, end=end)

Parameter Values

Parameter	Description
object(s)	Any object, and as many as you like. Will be converted to string before printed
sep=’separator‘	Optional. Specify how to separate the objects, if there is more than one. Default is ‘ ‘
end=’end‘	Optional. Specify what to print at the end. Default is ‘\n’ (line feed)

print("apple")
print("apple", "banana", "cherry")
print("apple", "banana", "cherry", sep="---")

Output:

apple
apple banana cherry
apple---banana---cherry

name = "Aman"
age = 16
print(name, age)

Output:

Aman 16

Using End (`end`)

Example:

print("Hello", end=" ")
print("World")

Output:

Hello World

8. Dynamic Typing

Python is a dynamically typed language.

This means:

No need to declare data type of variables.
Python automatically identifies the type.

Example:

x = 10
print(type(x))

x = "Hello"
print(type(x))

Output:

<class 'int'>
<class 'str'>

The same variable x stores different data types at different times.

9. Blocks and Indentation

Python uses indentation (spaces/tabs) to define blocks of code.

Indentation is very important in Python.

Example:

if 10 > 5:
    print("True")
    print("Inside if block")

print("Outside block")

Important Points

Usually 4 spaces are used for indentation.
Incorrect indentation gives error.

Wrong Example:

if 10 > 5:
print("Hello")

This causes:

IndentationError

10. Operators in Python

Operators perform operations on variables and values.

10.1 Arithmetic Operators

Operator	Meaning
+	Addition
–	Subtraction
*	Multiplication
/	Division
%	Modulus
//	Floor Division
**	Exponent

Example:

a = 10
b = 3

print(a + b)
print(a % b)
print(a ** b)

10.2 Relational Operators

Used for comparison.

Operator	Meaning
==	Equal
!=	Not Equal
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal

Example:

print(10 > 5)

Output:

True

10.3 Logical Operators

Operator	Meaning
and	Logical AND
or	Logical OR
not	Logical NOT

Example:

x = True
y = False

print(x and y)
print(x or y)

10.4 Assignment Operators

Operator	Example
=	x = 5
+=	x += 2
-=	x -= 2
*=	x *= 2

Example:

x = 5
x += 3
print(x)

Output:

10.5 Membership Operators

Operator	Meaning
in	Present
not in	Not Present

Example:

print("a" in "apple")

Output:

True

10.6 Identity Operators

Operator	Meaning
is	Same object
is not	Different object

Example:

x = 5
y = 5

print(x is y)

11. Expressions

An expression is a combination of Variables, Constants, Operators that produces a value.

Examples:

a + b
x * 5
10 > 3

Example Program:

a = 10
b = 20

c = a + b
print(c)

Output:

Summary

Python uses letters, digits, symbols, and spaces as character set.
Tokens are smallest units of Python program.
Variables store values.
Python supports dynamic typing.
Indentation defines code blocks.
Operators perform operations.
Expressions produce results.

Introduction to Python

1. Introduction to Python

2. Key Features of Python

3. Executing a “Hello World” Program

4. Python Execution Modes

A. Interactive Mode

B. Script Mode

1. Python Character Set

(i) Letters

(ii) Digits

(iii) Special Symbols

(iv) White Spaces

2. Python Tokens

2.1 Keywords

Important Points

2.2 Identifiers

Rules for Naming Identifiers

2.3 Literals

Types of Literals

(i) Numeric Literals

Types of Numeric Literals in Python

1. Integer Literals (int)

2. Floating Point Literals (float)

3. Complex Literals (complex)

Different Number Systems in Integer Literals

(i) Decimal Literal

(ii) Binary Literal

(iii) Octal Literal

(iv) Hexadecimal Literal

Important Points

Quick Revision

(ii) String Literals

(iii) Boolean Literals

(iv) Special Literal

2.4 Operators

2.5 Punctuators

3. Variables

4. Concept of l-value and r-value

l-value

r-value

5. Comments in Python

Types of Comments

(i) Single-line Comment

(ii) Multi-line Comment

6. Uses of Comments

7. print() Function

Syntax

print(object(s), sep=separator, end=end)

Parameter Values

Using End (end)

8. Dynamic Typing

9. Blocks and Indentation

Important Points

10. Operators in Python

10.1 Arithmetic Operators

10.2 Relational Operators

10.3 Logical Operators

10.4 Assignment Operators

10.5 Membership Operators

10.6 Identity Operators

11. Expressions

Summary

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1. Integer Literals (`int`)

2. Floating Point Literals (`float`)

3. Complex Literals (`complex`)

Using End (`end`)