⚡ Intermediate Level

# Creating lists
fruits = ["Apple", "Banana", "Mango", "Orange"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "Hello", 3.14, True]

# Accessing elements
print(fruits[0])    # Apple
print(fruits[-1])   # Orange
print(fruits[1:3])  # ['Banana', 'Mango']

# List methods
fruits.append("Grapes")       # Add at end
fruits.insert(1, "Kiwi")      # Add at index
fruits.remove("Banana")       # Remove by value
popped = fruits.pop()         # Remove last
fruits.sort()                 # Sort
fruits.reverse()              # Reverse
print(len(fruits))            # Length
print("Mango" in fruits)     # True — check membership

# List Comprehension — One-liner loop!
squares = [x**2 for x in range(1, 11)]
print(squares)  # [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

evens = [x for x in range(20) if x % 2 == 0]
print(evens)  # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# Tuple — cannot be changed (immutable)!
colors = ("Red", "Green", "Blue")
print(colors[0])    # Red
print(len(colors))  # 3

# Tuple unpacking
x, y, z = colors
print(x, y, z)  # Red Green Blue

# Single element tuple — must add comma!
single = (42,)  # ✅ Tuple
not_tuple = (42)  # ❌ Just an integer

# Tuple as dictionary key (list cannot be a key!)
locations = {(28.6, 77.2): "Delhi", (19.0, 72.8): "Mumbai"}

# Set — automatically removes duplicates!
nums = {1, 2, 3, 3, 4, 4, 5}
print(nums)  # {1, 2, 3, 4, 5}

# Set operations
a = {1, 2, 3, 4, 5}
b = {4, 5, 6, 7, 8}

print(a | b)   # Union: {1,2,3,4,5,6,7,8}
print(a & b)   # Intersection: {4, 5}
print(a - b)   # Difference: {1, 2, 3}
print(a ^ b)   # Symmetric diff: {1,2,3,6,7,8}

# Remove duplicates from list — Set trick!
my_list = [1, 2, 2, 3, 3, 3, 4]
unique = list(set(my_list))
print(unique)  # [1, 2, 3, 4]

# Creating dictionary
student = {
    "name": "Himanshu",
    "age": 20,
    "course": "B.Tech",
    "cgpa": 8.5,
    "skills": ["Python", "JavaScript", "SQL"]
}

# Access values
print(student["name"])        # Himanshu
print(student.get("age"))     # 20
print(student.get("phone", "Not found"))  # Not found

# Add/Update
student["city"] = "Delhi"       # Add new
student["age"] = 21             # Update
student.update({"phone": "9999999999"})

# Loop through 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}

# Nested Dictionary
students = {
    "student1": {"name": "Rahul", "marks": 85},
    "student2": {"name": "Priya", "marks": 92},
}
print(students["student2"]["name"])  # Priya

# Writing to a file
with open("notes.txt", "w") as f:
    f.write("Hello from PyMaster!\n")
    f.write("Python is awesome! 🐍\n")

# Reading a file
with open("notes.txt", "r") as f:
    content = f.read()
    print(content)

# Append to file
with open("notes.txt", "a") as f:
    f.write("New line added!\n")

# Read line by line
with open("notes.txt", "r") as f:
    for line in f:
        print(line.strip())

# Working with CSV
import csv
with open("data.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Age", "City"])
    writer.writerow(["Himanshu", 20, "Delhi"])

# Working with JSON
import json
data = {"name": "Himanshu", "skills": ["Python", "JS"]}
with open("data.json", "w") as f:
    json.dump(data, f, indent=2)

with open("data.json", "r") as f:
    loaded = json.load(f)
    print(loaded["name"])  # Himanshu

# Basic try/except
try:
    num = int(input("Enter number: "))
    result = 100 / num
    print(f"Result: {result}")
except ValueError:
    print("❌ Please enter a valid number!")
except ZeroDivisionError:
    print("❌ Cannot divide by zero!")
except Exception as e:
    print(f"❌ Error: {e}")
else:
    print("✅ No errors occurred!")
finally:
    print("🔄 This always runs!")

# Custom Exception
class AgeError(Exception):
    pass

def check_age(age):
    if age < 0:
        raise AgeError("Age cannot be negative!")
    if age > 150:
        raise AgeError("Age seems unrealistic!")
    print(f"Age {age} is valid ✅")

try:
    check_age(-5)
except AgeError as e:
    print(f"Error: {e}")

# Define a Class
class Student:
    def __init__(self, name, age, course):
        self.name = name
        self.age = age
        self.course = course

    def introduce(self):
        print(f"Hi! I'm {self.name}, {self.age} yrs, studying {self.course}")

    def is_adult(self):
        return self.age >= 18

# Create Objects
s1 = Student("Himanshu", 20, "B.Tech")
s2 = Student("Priya", 17, "12th")

s1.introduce()  # Hi! I'm Himanshu, 20 yrs, studying B.Tech
print(s1.is_adult())  # True
print(s2.is_adult())  # False

class Animal:
    def __init__(self, name):
        self.name = name
    def speak(self):
        return "..."

class Dog(Animal):
    def speak(self):
        return f"{self.name} says: Woof! 🐕"

class Cat(Animal):
    def speak(self):
        return f"{self.name} says: Meow! 🐱"

# Polymorphism — same method, different behavior!
animals = [Dog("Buddy"), Cat("Whiskers"), Dog("Max")]
for animal in animals:
    print(animal.speak())
# Buddy says: Woof! 🐕
# Whiskers says: Meow! 🐱
# Max says: Woof! 🐕