Class 9 AI Chapter - Python Topic - Tokens

 

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Chapter - Introduction to Python 
Other Topics

• Python Features
• Token Operators 
• Control Statements 
• Operator, Errors 
• Functions 

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Python Character Set

The character set in Python includes letters, digits, whitespace, special symbols, and Unicode characters. It allows writing code using English alphabets, numbers, operators, and punctuation marks.

1. Letters

Python supports both uppercase (A–Z) and lowercase (a–z) letters. These are used in identifiers like variable and function names.

Example:

Name = "Alvin"
language = "Python"

---

2. Digits

Python uses digits 0 to 9 in numeric literals and identifiers.

Example:

age = 25
roll_no1 = 101

---

3. Special Symbols

Python uses various symbols to define expressions, statements, and blocks.

Examples:

+ - * / = == != < > ( ) [ ] { } : , . #

Used in arithmetic and logical operations:

a = 10
if a > 5:
    print("Greater")

---

4. Whitespace Characters

Spaces, tabs (\t), and newlines (\n) are used to separate code elements and format blocks (like indentation).

Example:

if True:
    print("Indented block")

---

5. Unicode Characters

Python supports Unicode, allowing use of characters from all languages and even emojis.

Example:

greet = "नमस्ते"
smile = "😊"

---

Statements in Python

A statement in programming is a single instruction that performs a specific action, such as assigning a value, printing output, or making a decision. It is the smallest executable part of a program. Statements are executed in sequence unless control flow alters their order using conditions or loops.

1. Simple Statement

A simple statement is a single line of code that performs a specific action.

Example:

x = 10
print("Hello, World!")

2. Multiple Statement

Multiple statements are written on a single line, separated by semicolons (;). This is not recommended for readability but is allowed.

Example:

a = 5; b = 10; print(a + b)

3. Conditional Statement

Conditional statements are used for decision-making. They execute code based on certain conditions using if, elif, and else.

Example:

x = 15
if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

4. Iterative Statement

An iterative statement is used to execute a block of code repeatedly as long as a given condition is true. These are also called loops.

Common iterative statements in Python:

• for loop
• while loop

Example using for loop:

# Print numbers from 1 to 5
for i in range(1, 6):
    print(i)

Output:

1
2
3
4
5

This loop repeats 5 times, printing numbers from 1 to 5.

These types of statements help control the flow and logic of a Python program efficiently.

Comments in Python

Comments are used to explain code and make it easier to understand. They are ignored by the Python interpreter and do not affect program output.

1. Single-Line Comment

A single-line comment starts with the hash symbol #. It is used to write short notes or explanations.

Example:

# This is a single-line comment
x = 5  # Assigning value to x

2. Multi-Line Comment

Python doesn't have a true multi-line comment, but you can use multiple # symbols or triple quotes (''' or """) for block-style comments.

Example using multiple #:

# This is a multi-line comment
# explaining what the code does
# line by line.

Example using triple quotes (commonly for docstrings):

"""
This is a multi-line comment
using triple quotes.
Useful for large descriptions.
"""

Note: Triple-quoted comments are treated as strings, so they're only ignored if not assigned to a variable.

Token in Python

A token is the smallest unit of a Python program. Python breaks each line of code into meaningful pieces called tokens. These include keywords, identifiers, literals, operators, and punctuators.

1. Keywords

These are reserved words in Python that have special meaning. They cannot be used as variable names.

Examples:

if, else, while, for, def, return, True, False, None

Code Example:

if age > 18:
    print("Adult")

---

2. Identifiers

These are the names used for variables, functions, classes, etc.

Example:

name = "Alvin"
def greet():
    print("Hello")

---

3. Literals

These are constant values assigned to variables. Types include:

• String: "hello"
• Integer: 10
• Float: 3.14
• Boolean: True / False

Example:

x = 100
name = "Lily"

---

4. Operators

Used to perform operations on values or variables.

Examples: +, -, *, /, ==, >, <

Code Example:

a = 5 + 3

---

5. Punctuators (Separators)

Symbols that help structure the code.

Examples: (), :, ,, {}, []

Code Example:

def add(a, b):
    return a + b

---

6. Variable in Python

A variable in Python is used to store data that can be used and changed later in a program.

Key Points:

• Variables do not need declaration before use.
• Python is dynamically typed, so no need to declare data type.
• Use = to assign a value to a variable.

Syntax Example:

name = "Alvin"
age = 25
is_student = True

Variable Naming Rules:

• Must begin with a letter (A–Z or a–z) or an underscore (_)
• Cannot start with a number
• Case-sensitive (Name and name are different)
• Cannot use Python keywords (like if, for, while)

Example:

x = 10
y = 20
sum = x + y
print("Sum:", sum)

These tokens are combined to form valid Python programs. 

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Operator in Python

An operator is a special symbol that performs operations on variables and values. Python supports different types of operators for arithmetic, comparison, logic, assignment, and more.

1. Arithmetic Operators

Used to perform basic mathematical operations.

Operator	Description	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
//	Floor Division	a // b
%	Modulus	a % b
**	Exponentiation	a ** b

Example:

a = 10
b = 3
print(a + b)   # 13
print(a ** b)  # 1000

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2. Assignment Operators

Used to assign values to variables.

Operator	Meaning
=	Assign
+=	Add and assign
-=	Subtract and assign
*=	Multiply and assign

Example:

x = 5
x += 3  # Same as x = x + 3
print(x)  # 8

---

3. Comparison Operators

Used to compare two values.

Operator	Meaning	Example
==	Equal to	a == b
!=	Not equal	a != b
>	Greater than	a > b
<	Less than	a < b
>=	Greater or equal	a >= b
<=	Less or equal	a <= b

Example:

a = 10
b = 5
print(a > b)  # True

---

4. Logical Operators

Used to combine conditional statements.

Operator	Description
and	True if both are true
or	True if at least one is true
not	Inverts the result

Example:

x = 5
print(x > 3 and x < 10)  # True

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5. Bitwise Operators

Operate on bits directly.

Operator	Description
&	AND
`	`
^	XOR
~	NOT
<<	Left shift
>>	Right shift

Example:

a = 5      # 0101
b = 3      # 0011
print(a & b)  # 1 (0001)