Class 11 Python: Basics of Python Programming

 Class 11 Python: Basics of Python Programming

Understanding the structure and basic elements of a Python program is essential for writing clear and efficient code. Below is an overview of key concepts including program structure, indentation, identifiers, keywords, constants, variables, and operators.

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1. Structure of a Python Program

A Python program typically consists of:

• Statements: Instructions executed by the Python interpreter.
• Functions: Blocks of code designed to perform a specific task.
• Classes: Templates for creating objects (a particular data structure).
• Modules: Separate files containing Python code that can be imported into other programs.

Basic Structure Example:

# Importing a module
import math
# Function definition
def greet(name):
    print("Hello", name)
# Main program
greet("Alice")
print("The square root of 16 is", math.sqrt(16))

2. Indentation

Indentation refers to the spaces or tabs at the beginning of a line. In Python, indentation is crucial as it defines the structure of the code. Unlike other programming languages that use braces {}, Python uses indentation to group statements.

• Example:

  if 5 > 2:
      print("Five is greater than two.")

• Incorrect Indentation Example:

  if 5 > 2:
  print("Five is greater than two.")  # This will cause an error

Key Points:

• Consistent indentation is necessary.
• Typically, 4 spaces are used per indentation level.

3. Identifiers

Identifiers are names given to entities like variables, functions, classes, etc. in a program.

Rules for Identifiers:

• Can include letters (a-z, A-Z), digits (0-9), and underscores (_).
• Must not start with a digit.
• Are case-sensitive (name and Name are different).

Examples:

valid_name = 10
_valid_name = 20
name2 = 30

Invalid Identifiers:

2name = 10  # Starts with a digit, invalid
name@ = 20  # Contains special character, invalid

4. Keywords

Keywords are reserved words in Python that have special meanings. They cannot be used as identifiers.

Some Common Python Keywords:

• if, else, elif, for, while, break, continue
• def, return, import, from, as
• class, try, except, finally
• True, False, None

Example:

if True:
    print("This is a valid use of the 'if' keyword.")

5. Constants

Constants are variables whose values do not change throughout the program. Python does not have built-in constant types, but by convention, uppercase letters are used to denote a constant.

Example:

PI = 3.14159
GRAVITY = 9.8

6. Variables

Variables are used to store data that can be changed during program execution. Variables in Python do not need explicit declaration; they are created when a value is assigned.

Example:

age = 21
name = "John"

7. Types of Operators

Operators are symbols that perform operations on variables and values. Python supports several types of operators:

a. Arithmetic Operators

• Addition (+), Subtraction (-), Multiplication (*), Division (/)
• Modulus (%): Returns the remainder of a division
• Exponentiation (**): Raises a number to the power of another
• Floor Division (//): Division that results in the largest integer less than or equal to the result

Example:

a = 10
b = 3
print(a + b)  # 13
print(a - b)  # 7
print(a * b)  # 30
print(a / b)  # 3.3333
print(a % b)  # 1
print(a ** b)  # 1000
print(a // b)  # 3

b. Comparison Operators

• Used to compare two values and return a Boolean value (True or False).
• Equal (==), Not Equal (!=)
• Greater than (>), Less than (<)
• Greater than or equal to (>=), Less than or equal to (<=)

Example:

x = 10
y = 20
print(x == y)  # False
print(x != y)  # True
print(x > y)  # False
print(x < y)  # True

c. Logical Operators

• and: Returns True if both statements are true.
• or: Returns True if one of the statements is true.
• not: Reverses the result, returns False if the result is true.

Example:

x = True
y = False
print(x and y)  # False
print(x or y)  # True
print(not x)  # False

d. Assignment Operators

• Used to assign values to variables.
• Basic Assignment (=), Addition Assignment (+=), Subtraction Assignment (-=), Multiplication Assignment (*=), Division Assignment (/=)

Example:

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

e. Membership Operators

• in: Returns True if a sequence with the specified value is present in the object.
• not in: Returns True if a sequence with the specified value is not present in the object.

Example:

fruits = ["apple", "banana", "cherry"]
print("banana" in fruits)  # True
print("grape" not in fruits)  # True

Summary

• Structure of a Program: Includes statements, functions, classes, and modules.
• Indentation: Defines the structure of the code.
• Identifiers: Names given to variables, functions, etc.
• Keywords: Reserved words with special meanings.
• Constants: Variables with values that don't change (by convention).
• Variables: Containers for storing data.
• Operators: Symbols that perform operations on variables and values.