🔹 Python Basics – Learn with Code Examples & Comments

This guide covers essential Python concepts with detailed explanations and code examples for Lists, Dictionaries, Loops, and Functions.

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1️⃣ Lists in Python

A list is an ordered, mutable (changeable) collection of elements. It can store multiple data types.

🔹 Creating Lists

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

# Mixed data types
random_list = [10, "hello", 3.14, True]

# Empty list
empty_list = []

🔹 Accessing List Elements

fruits = ["apple", "banana", "cherry"]

print(fruits[0])  # Output: apple (first element)
print(fruits[-1]) # Output: cherry (last element)

🔹 Modifying Lists

fruits = ["apple", "banana", "cherry"]

# Changing an element
fruits[1] = "orange"
print(fruits)  # Output: ['apple', 'orange', 'cherry']

# Adding elements
fruits.append("grapes")  # Adds to the end
print(fruits)

fruits.insert(1, "blueberry")  # Adds at index 1
print(fruits)

# Removing elements
fruits.remove("apple")  # Removes by value
print(fruits)

deleted_item = fruits.pop(2)  # Removes item at index 2
print(f"Removed: {deleted_item}")

🔹 List Slicing

numbers = [0, 1, 2, 3, 4, 5, 6, 7]

print(numbers[2:5])   # Output: [2, 3, 4] (index 2 to 4)
print(numbers[:4])    # Output: [0, 1, 2, 3] (start to index 3)
print(numbers[3:])    # Output: [3, 4, 5, 6, 7] (index 3 to end)
print(numbers[::2])   # Output: [0, 2, 4, 6] (step of 2)

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2️⃣ Dictionaries in Python

A dictionary is an unordered collection of key-value pairs.

🔹 Creating a Dictionary

# Creating a dictionary
student = {
    "name": "John",
    "age": 20,
    "grade": "A",
    "subjects": ["Math", "Science"]
}

# Accessing values
print(student["name"])  # Output: John
print(student.get("age"))  # Output: 20

🔹 Modifying a Dictionary

student["age"] = 21  # Modifying an existing key
student["city"] = "New York"  # Adding a new key
print(student)

🔹 Deleting a Key

del student["grade"]  # Removes 'grade' key
print(student)

removed_value = student.pop("age")  # Removes and returns the value
print(f"Removed Age: {removed_value}")

🔹 Looping Through a Dictionary

for key, value in student.items():
    print(f"{key}: {value}")

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3️⃣ Loops in Python

🔹 for Loop

Used to iterate over sequences like lists, strings, and dictionaries.

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(f"I like {fruit}")  

Looping with range()

for i in range(5):  # Loops from 0 to 4
    print(i)

Looping Through a Dictionary

student = {"name": "John", "age": 20, "grade": "A"}

for key, value in student.items():
    print(f"{key}: {value}")

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🔹 while Loop

Used when the number of iterations is unknown.

x = 0
while x < 5:
    print(f"x is {x}")
    x += 1  # Incrementing x

🔹 break and continue

• break: Stops the loop.
• continue: Skips the current iteration.

for num in range(10):
    if num == 5:
        break  # Stops when num is 5
    print(num)

for num in range(5):
    if num == 2:
        continue  # Skips 2
    print(num)

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4️⃣ Functions in Python

A function is a reusable block of code that performs a specific task.

🔹 Defining and Calling Functions

def greet():
    print("Hello, welcome!")

greet()  # Calling the function

🔹 Function with Parameters

def greet_user(name):
    print(f"Hello, {name}!")

greet_user("Alice")  # Output: Hello, Alice!

🔹 Function with Return Value

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

result = add(3, 5)
print(result)  # Output: 8

🔹 Default Arguments

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

greet()       # Output: Hello, Guest!
greet("Alex") # Output: Hello, Alex!

🔹 Lambda Functions (Anonymous Functions)

square = lambda x: x * x
print(square(4))  # Output: 16

add = lambda a, b: a + b
print(add(3, 7))  # Output: 10

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🔥 Summary

✅ Lists → Ordered, mutable collection. Supports indexing, slicing, modification.
✅ Dictionaries → Unordered, key-value pairs. Fast lookups.
✅ Loops → for and while loops for iteration. Use break & continue.
✅ Functions → Code reusability, parameters, return values, default arguments, lambda functions.

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🚀 Happy Coding! 🎯