Python_basics 3.ipynb

Kernel: Python 3 (ipykernel)

Python Basics -

In this notebook, we will continue learning Python fundamentals: conditions, loops, functions, and lists.

Conditional Statements

Python uses if, elif, and else to make decisions based on conditions.

9+8 

   print(9+8)

#only if 
age = int(input("Enter your age:"))

if age >= 18:
    print("You are eligible to vote.")

# Example: ifelse
marks=int(input("Enter your marks"))

if marks >= 50:
    print("You passed the exam.")
else:
    print("You failed the exam.")

#if-elif-else
temperature = 32

if temperature > 35:
    print("It's very hot outside.")
elif temperature >= 20:
    print("Weather is pleasant.")
else:
    print("It's cold outside.")

#Nested If 
age=int(input("Enter your age:"))
citizen = True

if age >= 18:
    if citizen:
        print("You are eligible to vote.")
    else:
        print("You must be a citizen to vote.")
else:
    print("You are too young to vote.")

Case Study: Online Shopping Discount System

Scenario: An e-commerce platform wants to apply discounts based on the customer’s cart value and membership status.

Rules:

• If the cart value is above ₹5000:

• If the customer is a Premium Member, apply 20% discount.

• If the customer is a Regular Member, apply 10% discount.

• If the cart value is between ₹2000 and ₹5000, apply 5% discount for everyone.

• Otherwise, no discount.

# Online Shopping Discount System

print("Welcome to the E-Commerce Discount Calculator!\n")

# Get user input
try:
    cart_value = float(input("Enter your cart value (in ₹): "))
    membership = input("Enter your membership type (Premium/Regular/None): ").strip().lower()

    discount = 0

    # Apply discount rules
    if cart_value > 5000:
        if membership == "premium":
            discount = 0.20
        elif membership == "regular":
            discount = 0.10
        else:
            discount = 0
    elif 2000 <= cart_value <= 5000:
        discount = 0.05
    else:
        discount = 0

    # Calculate final price
    discount_amount = cart_value * discount
    final_price = cart_value - discount_amount

    # Display results
    print("\n--- Discount Summary ---")
    print(f"Original Cart Value: ₹{cart_value:.2f}")
    print(f"Discount Applied: ₹{discount_amount:.2f}")
    print(f"Final Price to Pay: ₹{final_price:.2f}")

except ValueError:
    print("end")

cart_value = int(input("Enter the Cart value:"))
membership = "Premium"  # Options: "Premium" or "Regular"

if cart_value > 5000:
    if membership == "Premium":
        discount = 0.20 * cart_value
        print("Premium member discount applied: ₹", discount)
    else:
        discount = 0.10 * cart_value
        print("Regular member discount applied: ₹", discount)
elif cart_value >= 2000:
    discount = 0.05 * cart_value
    print("5% discount applied: ₹", discount)
else:
    discount = 0
    print("No discount available.")

print("Final Price: ₹", cart_value - discount)

Loops

Python has two main types of loops:

• for loop (used to iterate over a sequence)

• while loop (used to repeat as long as a condition is true)

# Example: While loop
count = 0
while count < 5:
    print("Count:", count)
    count += 1

a=list(range(20,10,-2))
a

# Example: For loop
for i in range(5):
    print("Iteration:", i)

## Iteraing through a list
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    name=input("Enter your name: ")

## Using Range function
for i in range(5):
    print("Number:", i)

## Looping through Strings
word = "Python"

for letter in word:
    print(letter)

##Nested for loop
for i in range(1, 4):
    for j in range(1, 4):
        print(f"{i} x {j} = {i*j}")

##Using for with if (conditional inside loop)
numbers = [1, 5, 10, 12, 15]

for num in numbers:
    if num % 2 == 0:
        print(num, "is even")
    else:
        print(num, "is odd")

Expanded & Interactive Case Study: Online Shopping Discount System

Scenario:

• An e-commerce platform applies discounts based on cart value, membership, and promo codes.

• Users can also buy multiple items, and the program calculates the total price per item and overall bill summary.

# Sample item catalog
items = {
    "Laptop": 45000,
    "Headphones": 1500,
    "Mouse": 800,
    "Keyboard": 1200,
    "Smartphone": 25000
}

# User inputs
membership = input("Enter membership type (Premium/Regular): ")
cart = {}  # item_name: quantity

print("\nAvailable items:")
for item, price in items.items():
    print(f"{item}: ₹{price}")

# Let user choose multiple items
while True:
    chosen_item = input("\nEnter item name to add to cart (or 'done' to finish): ")
    if chosen_item.lower() == "done":
        break
    if chosen_item in items:
        quantity = int(input(f"Enter quantity for {chosen_item}: "))
        cart[chosen_item] = quantity
    else:
        print("Item not available!")

# Calculate total
total = 0
print("\nCart Summary:")
for item, quantity in cart.items():
    item_total = items[item] * quantity
    print(f"{item} x {quantity} = ₹{item_total}")
    total += item_total

# Apply discount rules
if total > 5000:
    if membership.lower() == "premium":
        discount = 0.20 * total
        print("\nPremium member discount applied: ₹", discount)
    else:
        discount = 0.10 * total
        print("\nRegular member discount applied: ₹", discount)
elif total >= 2000:
    discount = 0.05 * total
    print("\n5% discount applied: ₹", discount)
else:
    discount = 0
    print("\nNo discount available.")

final_price = total - discount
print("\nTotal Bill: ₹", total)
print("Discount: ₹", discount)
print("Amount to Pay: ₹", final_price)

## USER INPOUT lists
# Create an empty list
user_list = []

# Ask how many items the user wants to add
n = int(input("How many items do you want to add to the list? "))

# Loop to take input
for i in range(n):
    item = input(f"Enter item {i+1}: ")
    user_list.append(item)

print("Your list:", user_list)

d={"A":1,"B": 2}
d["C"]=7

## User Input dictionary 
# Create an empty dictionary
user_dict = {}

# Ask how many key-value pairs
n = int(input("\nHow many key-value pairs do you want to add? "))

# Loop to take input
for i in range(n):
    key = input(f"Enter key {i+1}: ")
    value = input(f"Enter value for '{key}': ")
    user_dict[key] = value

print("Your dictionary:", user_dict)

Functions

Functions are reusable blocks of code defined using the def keyword.

1. Functions Without Variables

These functions don’t take any input and may or may not return something.

# Example 1: Simple function with no input and no output
def greet():
    print("Hello, welcome to Python!")

greet()   # Output: Hello, welcome to Python!


# Example 2: Function with no input but returns a value
def get_pi():
    return 3.14159

print(get_pi())  # Output: 3.14159

Hello, welcome to Python!
3.14159

2. Functions With Variables (Parameters)

These allow reusability by passing arguments.

# Example 1: Function with one variable
def square(num):
    return num ** 2

square(12)  

144

# Example 2: Function with multiple variables
def EUI(a, b):
    return 2*a + b

print(EUI(3, 7))   
print(EUI(13, 27)) 

13
53

3. Functions With Default Parameters

Parameters can have default values.

def greet(name="Guest"):
    print(f"Hello, {name}!")

greet()           
greet("Suyashi")  

Hello, Guest!
Hello, Suyashi!

greet("Aman")

Hello, Aman!

4. Functions With Variable-Length Arguments

When the number of arguments is not fixed.

# *args (positional arguments)
def add_all(*numbers):
    return sum(numbers)

print(add_all(2, 3, 5, 7,8,9,80))  

114

# **kwargs (keyword arguments)
def show_info(**details):
    for key, value in details.items():
        print(f"{key}: {value}")

show_info(name="Riya", age=25, city="Delhi")

name: Riya
age: 25
city: Delhi

5. Lambda (Anonymous) Functions

Small, one-line functions.

# With Single Variable 
power_4 = lambda x:x**4
power_4(8)

4096

# With three variable s
equi = lambda x,y,z:(2**x+3*y+z)
equi(2,2,3)

13

# Without variables
hello = lambda: "Hello World"
print(hello())  

Case Study: Simple Student Grading System

Create different functions to handle student grades System

Interactive Extension

• Createa Grading Interface

• Add all subject marks

• Take avaearge of it

• Classify learners as Excellent, Good, Average , Poor

• Print their score sheet

# Function without variables
def welcome():
    print("Welcome to Student Grading System")

# Function with variables
def calculate_percentage(marks_obtained, total_marks):
    return (marks_obtained / total_marks) * 100

# Function with default parameter
def assign_grade(percentage, pass_mark=40):
    if percentage >= 90:
        return "A+"
    elif percentage >= 75:
        return "A"
    elif percentage >= 60:
        return "B"
    elif percentage >= pass_mark:
        return "C"
    else:
        return "Fail"

# Function with *args
def average_marks(*marks):
    return sum(marks) / len(marks)

# Lambda function
status = lambda grade: "Pass" if grade != "Fail" else "Fail"

# --------------------
# Running the case study
welcome()

avg = average_marks(78, 85, 69, 92)
percentage = calculate_percentage(avg, 100)
grade = assign_grade(percentage)

print(f"Average Marks: {avg}")
print(f"Percentage: {percentage:.2f}%")
print(f"Grade: {grade}")
print(f"Status: {status(grade)}")

Hands-on Quick Practice

Try solving the following problems:

1. Write a program that checks whether a number entered by the user is even or odd.

2. Use a loop to print the first 10 natural numbers.

3. Write a function that takes two numbers and returns their sum.

4. Write a Python program to take n items from the user and store them in a list. Then Print the list Print the number of items that start with the letter 'a'

5. Write a Python program to create a dictionary from user input. The user should enter n key-value pairs, where the value is an integer. Then:

   • Print the dictionary

   • Print the sum of all values in the dictionar

# Write your practice code here