print("Hello, World!")

# Correct indentation
if True:
    print("This is indented correctly")
    print("This line is also inside the if block")

print("This line is outside the if block")

# This is a single-line comment

"""
This is a
multi-line comment
(technically a multi-line string used as a comment)
"""

print("Comments make code readable!")  # Inline comment

# Python — clean and simple
name = "Alice"
age = 25
print(name)

# You CAN write multiple statements on one line with semicolons (not recommended)
x = 1; y = 2; z = 3

# Python automatically detects the data type
name = "Alice"          # String
age = 25                # Integer
height = 5.7            # Float
is_student = True       # Boolean

print(name)
print(age)
print(height)
print(is_student)

first_name = "John"
last_name = 'Doe'
full_name = first_name + " " + last_name  # String concatenation
print(full_name)  # Output: John Doe

# String methods
message = "hello, world!"
print(message.upper())        # HELLO, WORLD!
print(message.capitalize())   # Hello, world!
print(message.replace("world", "Python"))  # hello, Python!
print(len(message))           # 13 (length of string)

# String formatting (f-strings — the modern way)
name = "Alice"
age = 25
print(f"My name is {name} and I am {age} years old.")
# Output: My name is Alice and I am 25 years old.

x = 10
y = -5
z = 0

print(x + y)   # 5  (addition)
print(x - y)   # 15 (subtraction)
print(x * y)   # -50 (multiplication)
print(x // y)  # -2  (floor division)
print(x % 3)   # 1   (modulus — remainder)
print(x ** 2)  # 100 (exponentiation — 10 squared)

pi = 3.14159
price = 99.99
temperature = -10.5

# Rounding
print(round(pi, 2))  # 3.14

# Converting between types
age = 25
print(float(age))    # 25.0
print(int(3.9))      # 3 (truncates, doesn't round)

is_raining = True
is_sunny = False

print(is_raining)          # True
print(type(is_raining))    # <class 'bool'>
print(10 > 5)              # True
print(10 == 5)             # False
print(not is_raining)      # False

result = None
print(result)           # None
print(result is None)   # True

x = 42
print(type(x))          # <class 'int'>

# Type conversion
print(str(x))           # "42" — integer to string
print(float(x))         # 42.0 — integer to float

name = "123"
print(int(name))        # 123 — string to integer (only works if string is a number)

# Creating a list
fruits = ["apple", "banana", "cherry", "mango"]

# Accessing items (indexing starts at 0)
print(fruits[0])    # apple
print(fruits[-1])   # mango (negative index — from the end)

# Slicing
print(fruits[1:3])  # ['banana', 'cherry']

# Modifying lists
fruits.append("orange")     # Add to end
fruits.insert(1, "grape")   # Insert at position 1
fruits.remove("banana")     # Remove specific item
fruits.pop()                # Remove last item
fruits.sort()               # Sort alphabetically

print(len(fruits))          # Number of items in list

# Looping through a list
for fruit in fruits:
    print(fruit)

# List comprehension — a powerful Python feature
squares = [x**2 for x in range(1, 6)]
print(squares)  # [1, 4, 9, 16, 25]

# Creating a tuple
coordinates = (10.5, 20.3)
colors = ("red", "green", "blue")

print(coordinates[0])   # 10.5
print(len(colors))      # 3

# Tuple unpacking
x, y = coordinates
print(x)  # 10.5
print(y)  # 20.3

# Tuples cannot be changed
# colors[0] = "yellow"  # This would raise a TypeError!

# Creating a set
numbers = {1, 2, 3, 4, 4, 5, 5}
print(numbers)  # {1, 2, 3, 4, 5} — duplicates removed automatically!

# Set operations
set_a = {1, 2, 3, 4}
set_b = {3, 4, 5, 6}

print(set_a | set_b)   # Union: {1, 2, 3, 4, 5, 6}
print(set_a & set_b)   # Intersection: {3, 4}
print(set_a - set_b)   # Difference: {1, 2}

# Adding and removing
numbers.add(6)
numbers.discard(1)

# Creating a dictionary
student = {
    "name": "Alice",
    "age": 22,
    "grade": "A",
    "courses": ["Math", "Science", "Python"]
}

# Accessing values
print(student["name"])          # Alice
print(student.get("age"))       # 22
print(student.get("email", "Not Found"))  # Not Found (safe access with default)

# Modifying dictionaries
student["email"] = "alice@example.com"  # Add new key
student["age"] = 23                     # Update existing key
del student["grade"]                    # Delete a key

# Looping through a dictionary
for key, value in student.items():
    print(f"{key}: {value}")

# Dictionary comprehension
squares = {x: x**2 for x in range(1, 6)}
print(squares)  # {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

age = 20

if age < 13:
    print("Child")
elif age < 18:
    print("Teenager")
elif age < 65:
    print("Adult")
else:
    print("Senior")

# Output: Adult

x = 10
y = 20

print(x == y)   # False — Equal to
print(x != y)   # True  — Not equal to
print(x < y)    # True  — Less than
print(x > y)    # False — Greater than
print(x <= y)   # True  — Less than or equal
print(x >= y)   # False — Greater than or equal

age = 25
income = 50000

# and — both conditions must be True
if age >= 18 and income >= 30000:
    print("Eligible for loan")

# or — at least one condition must be True
if age < 18 or income < 10000:
    print("Not eligible")

# not — reverses the condition
is_raining = True
if not is_raining:
    print("Let's go outside!")
else:
    print("Stay indoors")

age = 20
status = "Adult" if age >= 18 else "Minor"
print(status)  # Adult

# Loop through a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# Loop through a range of numbers
for i in range(5):          # 0, 1, 2, 3, 4
    print(i)

for i in range(1, 11):      # 1 to 10
    print(i)

for i in range(0, 20, 2):   # 0, 2, 4, 6... (step of 2)
    print(i)

# Loop with enumerate (get index AND value)
colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(f"{index}: {color}")
# Output: 0: red, 1: green, 2: blue

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

# while loop — repeats as long as condition is True
count = 0
while count < 5:
    print(f"Count: {count}")
    count += 1  # Increment to avoid infinite loop

# while with user input
password = ""
while password != "python123":
    password = input("Enter password: ")
print("Access granted!")

# break — exits the loop immediately
for i in range(10):
    if i == 5:
        break       # Stop when i equals 5
    print(i)        # Prints 0, 1, 2, 3, 4

# continue — skips current iteration
for i in range(10):
    if i % 2 == 0:
        continue    # Skip even numbers
    print(i)        # Prints 1, 3, 5, 7, 9

# pass — does nothing (placeholder)
for i in range(5):
    pass            # Empty loop — no error

# Define a function
def greet():
    print("Hello! Welcome to Python programming.")

# Call (execute) the function
greet()  # Output: Hello! Welcome to Python programming.

def greet_user(name):
    print(f"Hello, {name}! Welcome to elearncourses.com")

greet_user("Alice")   # Hello, Alice! Welcome to elearncourses.com
greet_user("Bob")     # Hello, Bob! Welcome to elearncourses.com

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

result = add_numbers(5, 3)
print(result)  # 8

def calculate_area(length, width):
    area = length * width
    return area

print(calculate_area(10, 5))  # 50

def greet(name, message="Good morning"):
    print(f"{message}, {name}!")

greet("Alice")                    # Good morning, Alice!
greet("Bob", "Good evening")      # Good evening, Bob!

# *args — accept any number of positional arguments
def sum_all(*numbers):
    total = 0
    for num in numbers:
        total += num
    return total

print(sum_all(1, 2, 3))           # 6
print(sum_all(10, 20, 30, 40))    # 100

# **kwargs — accept any number of keyword arguments
def display_info(**info):
    for key, value in info.items():
        print(f"{key}: {value}")

display_info(name="Alice", age=25, city="Hyderabad")

# Regular function
def square(x):
    return x ** 2

# Equivalent lambda function
square = lambda x: x ** 2
print(square(5))  # 25

# Lambda with multiple parameters
add = lambda x, y: x + y
print(add(3, 4))  # 7

# Common use: sorting with lambda
students = [("Alice", 85), ("Bob", 92), ("Charlie", 78)]
students.sort(key=lambda student: student[1])  # Sort by grade
print(students)  # [('Charlie', 78), ('Alice', 85), ('Bob', 92)]

# Define a class
class Student:
    # Constructor method — called when creating an object
    def __init__(self, name, age, grade):
        self.name = name      # Instance attributes
        self.age = age
        self.grade = grade

    # Instance method
    def introduce(self):
        print(f"Hi, I'm {self.name}, {self.age} years old, studying in Grade {self.grade}.")

    def study(self, subject):
        print(f"{self.name} is studying {subject}.")

# Create objects (instances) of the Student class
student1 = Student("Alice", 20, "A")
student2 = Student("Bob", 22, "B")

# Call methods
student1.introduce()   # Hi, I'm Alice, 20 years old, studying in Grade A.
student2.introduce()   # Hi, I'm Bob, 22 years old, studying in Grade B.
student1.study("Python")  # Alice is studying Python.

# Access attributes
print(student1.name)   # Alice
print(student2.age)    # 22

# Parent class
class Animal:
    def __init__(self, name, species):
        self.name = name
        self.species = species

    def make_sound(self):
        print("Some generic animal sound")

    def describe(self):
        print(f"{self.name} is a {self.species}")

# Child class inheriting from Animal
class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name, "Dog")  # Call parent constructor
        self.breed = breed

    def make_sound(self):  # Override parent method (Polymorphism)
        print(f"{self.name} says: Woof! Woof!")

    def fetch(self, item):
        print(f"{self.name} fetches the {item}!")

class Cat(Animal):
    def make_sound(self):
        print(f"{self.name} says: Meow!")

# Create objects
dog = Dog("Buddy", "Golden Retriever")
cat = Cat("Whiskers", "Cat")

dog.describe()      # Buddy is a Dog
dog.make_sound()    # Buddy says: Woof! Woof!
dog.fetch("ball")   # Buddy fetches the ball!
cat.make_sound()    # Whiskers says: Meow!

# math module — mathematical functions
import math

print(math.pi)          # 3.141592653589793
print(math.sqrt(144))   # 12.0
print(math.ceil(4.2))   # 5
print(math.floor(4.9))  # 4
print(math.factorial(5))# 120

# random module — random number generation
import random

print(random.randint(1, 100))     # Random integer between 1 and 100
print(random.choice(["a", "b", "c"]))  # Random item from list
print(random.random())            # Random float between 0 and 1

# datetime module — date and time operations
from datetime import datetime, date

now = datetime.now()
print(now)                         # Current date and time
print(now.strftime("%d/%m/%Y"))    # Formatted date: 24/03/2025
print(date.today())                # Today's date

# os module — operating system interaction
import os

print(os.getcwd())         # Current working directory
print(os.listdir("."))     # Files in current directory
os.mkdir("new_folder")     # Create a directory

# Install a package
pip install requests

# Install multiple packages
pip install pandas numpy matplotlib

# List installed packages
pip list

# Uninstall a package
pip uninstall requests

# Writing to a file
with open("students.txt", "w") as file:
    file.write("Alice - Grade A\n")
    file.write("Bob - Grade B\n")
    file.write("Charlie - Grade A+\n")

# Reading an entire file
with open("students.txt", "r") as file:
    content = file.read()
    print(content)

# Reading line by line
with open("students.txt", "r") as file:
    for line in file:
        print(line.strip())

# Appending to a file
with open("students.txt", "a") as file:
    file.write("Diana - Grade A\n")

# Working with JSON files
import json

# Writing JSON
data = {
    "name": "Alice",
    "age": 22,
    "courses": ["Python", "Data Science"]
}

with open("student.json", "w") as file:
    json.dump(data, file, indent=4)

# Reading JSON
with open("student.json", "r") as file:
    loaded_data = json.load(file)
    print(loaded_data["name"])  # Alice

# Basic try-except
try:
    number = int(input("Enter a number: "))
    result = 100 / number
    print(f"Result: {result}")
except ValueError:
    print("Error: Please enter a valid number!")
except ZeroDivisionError:
    print("Error: Cannot divide by zero!")
except Exception as e:
    print(f"An unexpected error occurred: {e}")
finally:
    print("This block always runs, regardless of errors.")

# Raising custom exceptions
def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative!")
    if age > 150:
        raise ValueError("Age seems unrealistically high!")
    return age

try:
    validate_age(-5)
except ValueError as e:
    print(f"Validation Error: {e}")

import random

def number_guessing_game():
    secret_number = random.randint(1, 100)
    attempts = 0
    max_attempts = 7

    print("Welcome to the Number Guessing Game!")
    print(f"I'm thinking of a number between 1 and 100.")
    print(f"You have {max_attempts} attempts.\n")

    while attempts < max_attempts:
        try:
            guess = int(input(f"Attempt {attempts + 1}: Enter your guess: "))
            attempts += 1

            if guess < secret_number:
                print("Too low! Try higher.\n")
            elif guess > secret_number:
                print("Too high! Try lower.\n")
            else:
                print(f"🎉 Congratulations! You guessed it in {attempts} attempts!")
                return

        except ValueError:
            print("Please enter a valid number.\n")

    print(f"Game over! The number was {secret_number}.")

number_guessing_game()

def calculator():
    print("=== Python Calculator ===")
    print("Operations: +, -, *, /")

    try:
        num1 = float(input("Enter first number: "))
        operator = input("Enter operator (+, -, *, /): ")
        num2 = float(input("Enter second number: "))

        if operator == "+":
            result = num1 + num2
        elif operator == "-":
            result = num1 - num2
        elif operator == "*":
            result = num1 * num2
        elif operator == "/":
            if num2 == 0:
                print("Error: Cannot divide by zero!")
                return
            result = num1 / num2
        else:
            print("Invalid operator!")
            return

        print(f"\nResult: {num1} {operator} {num2} = {result}")

    except ValueError:
        print("Error: Please enter valid numbers.")

calculator()

def todo_app():
    tasks = []

    while True:
        print("\n=== To-Do List ===")
        print("1. View tasks")
        print("2. Add task")
        print("3. Complete task")
        print("4. Delete task")
        print("5. Exit")

        choice = input("\nEnter choice (1-5): ")

        if choice == "1":
            if not tasks:
                print("No tasks yet! Add some tasks.")
            else:
                print("\nYour Tasks:")
                for i, task in enumerate(tasks, 1):
                    status = "✓" if task["done"] else "○"
                    print(f"  {i}. [{status}] {task['name']}")

        elif choice == "2":
            task_name = input("Enter task name: ")
            tasks.append({"name": task_name, "done": False})
            print(f"✅ Task '{task_name}' added!")

        elif choice == "3":
            task_num = int(input("Enter task number to complete: ")) - 1
            if 0 <= task_num < len(tasks):
                tasks[task_num]["done"] = True
                print(f"✅ Task completed!")

        elif choice == "4":
            task_num = int(input("Enter task number to delete: ")) - 1
            if 0 <= task_num < len(tasks):
                removed = tasks.pop(task_num)
                print(f"🗑 Task '{removed['name']}' deleted!")

        elif choice == "5":
            print("Goodbye! Keep learning Python! 🐍")
            break

todo_app()