Python Variables

What is a Variable

A variable is a named container used to store data in memory. Program execution dynamic values handling ke liye memory spaces refer karti hai jise variable kehte hain.

Basic syntax for declaring a variable is:

variable_name = value

Basic Examples

full_name = "gagan"
print(full_name)

laptop = "asus"
print(laptop)

gagan = "teacher"
print(gagan)

Naming Rules & Conditions

Python variables standard syntax rules follow karte hain. In rules ko disregard karne par syntax errors arise hote hain:

1. Cannot start with a number: Variable names number se start nahi ho sakte (e.g. 1x invalid syntax par x1 valid hai).
2. No special characters except underscore (_): Variable names me special characters (like !, @, $, -, or spaces) allowed nahi hote. Faqat underscore (_) allowed hai (e.g. first_name valid, last name invalid).
3. Case-Sensitive: Python case-sensitive language hai. name aur Name do completely different variables treat hote hain.

Data Types in Python

Variables multiple types of values store kar sakte hain. Python auto-detects variable data types based on the value assigned:

• String (str): Sequence of characters enclosed in single quotes (' ') or double quotes (" ").
• Integer (int): Whole numbers without decimal points.
• Float (float): Decimal numbers.
• Boolean (bool): Stores only two truth values: True or False.

meri_city = "Chandigarh"
mera_naam = "gagan"
mere_marks = 98.9
gender_male = True
salary = "2220"

print(f"meri city ka naam {meri_city}, mera naam hai {mera_naam} aur mera marks {mere_marks} mera gender male hai = {gender_male} aur mera salary hai {salary}")

Taking User Input

Python me user se dynamic values fetch karne ke liye input() function use hota hai. Default behavior me input() hamesha string return karta hai. Numerical input ke liye type casting (int() ya float()) perform ki jaati hai.

Name = input("apna naam dalo = ")
age = int(input("apni age dalo = "))
print(f"Mera naam {Name} hai aur meri age {age} hai")

a = int(input("enter the first number = "))
b = int(input("enter the second number = "))
print(f"the output of a and b = {a + b}")

F-Strings Formatting

An f-string (formatted string literal) is used to insert variables or expressions inside a string using curly braces {}.

Syntax: f"sentence {variable}"

name = "lokesh"
gagan_ki_age = 18
height = 5.9

print(f"ludhiana wale ka naam {name} aur gagan ki age hai {gagan_ki_age} aur uski height hai {height}")

Variable Swapping

Python single line tuple unpacking mechanism se without temporary variable value swap support karta hai.

a = 10
b = 20

a, b = b, a

print("a =", a)
print("b =", b)

Practice Questions & Solutions

Comprehensive set of practice problems with solutions:

1. Print Name using F-String

name = "Ali"
print(f"My name is {name}")

2. Name and City

name = "Ali"
city = "Delhi"
print(f"My name is {name} and I live in {city}")

3. Sum / Subtraction of Two Numbers

a = 10
b = 5
print(f"inka minu = {a - b}")

4. Area of Rectangle

length = 10
width = 5
print(f"Area of rectangle is {length * width}")

5. Total Cost Calculation

price = 50
quantity = 3
print(f"Total cost = {price * quantity}")

6. Age Example

age = 21
print(f"I am {age} years old")

7. Mathematical Operations

a = 20
b = 4
print(f"Addition = {a + b}")
print(f"Subtraction = {a - b}")
print(f"Multiplication = {a * b}")
print(f"Division = {a / b}")

8. Student Marks from User Input

name = input("enter your name = ")
marks = int(input("enter your marks "))
print(f"Student ka naam {name} kya hai iska scored {marks} marks")

9. Area of Triangle

base = 10
height = 5
print(f"Area of triangle = {base * height}")

10. Average of Two Numbers

num1 = int(input("enter the first number = "))
num2 = int(input("enter the second number = "))
print(f"Average = {(num1 + num2) / 2}")

11. Sum of Two Inputs

num1 = int(input("enter the first number = "))
num2 = int(input("enter the second number = "))
print(f"sum of num and num2 = {num1 + num2}")

12. Rectangle Area from Input

length = int(input("Enter the length "))
breadth = int(input("Enter the breadth "))
print(f"area of recatngle is {length * breadth}")