Topic: Linked Lists in Python – Part 1: Introduction and Singly Linked List Basics

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What is a Linked List?

• A linked list is a linear data structure where each element (called a node) contains:

• The data value.
• A pointer (or reference) to the next node.

• Unlike arrays, linked lists don’t require contiguous memory and can grow dynamically.

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Why Use Linked Lists?

• Efficient insertions/deletions at the beginning or middle.
• No need for pre-defining size, unlike arrays.
• Used in memory-efficient applications like OS kernels, compilers, and real-time systems.

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Types of Linked Lists

• Singly Linked List – Each node points to the next.
• Doubly Linked List – Nodes have next and previous pointers.
• Circular Linked List – The last node points back to the head.

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Basic Structure of a Node

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

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Building a Singly Linked List

class LinkedList:
    def __init__(self):
        self.head = None

    def append(self, data):
        new_node = Node(data)

        if not self.head:
            self.head = new_node
            return

        current = self.head
        while current.next:
            current = current.next
        current.next = new_node

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Traversing the List

def display(self):
    current = self.head
    while current:
        print(current.data, end=" -> ")
        current = current.next
    print("None")

Usage:

ll = LinkedList()
ll.append(10)
ll.append(20)
ll.append(30)
ll.display()  # Output: 10 -> 20 -> 30 -> None

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Inserting at the Beginning

def insert_at_beginning(self, data):
    new_node = Node(data)
    new_node.next = self.head
    self.head = new_node

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Summary

• A singly linked list stores data as a sequence of nodes linked by references.

• Supports dynamic memory usage, fast insertions, and flexible resizing.

• The key is managing node connections safely and efficiently.

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Exercise

• Implement a method length() that returns the number of nodes in the list.

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#DataStructures #LinkedList #DSA #Python #CodingBasics

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Topic: Python Functions – Part 1 of 3: Basics, Syntax, and Parameters (Long Lesson)

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### 1. What is a Function in Python?

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

• Avoid code duplication
• Improve code readability
• Enable modular programming

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### 2. Why Use Functions?

• Reusability – Write once, use many times
• Modularity – Split large tasks into smaller blocks
• Debuggability – Easier to test/debug small units
• Abstraction – Hide complex logic behind a name

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### 3. Function Syntax

def function_name(parameters):
    # block of code
    return result

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### 4. Creating a Simple Function

def greet():
    print("Hello, welcome to Python functions!")
    
greet()  # Calling the function

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### 5. Function with Parameters

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

greet_user("Hussein")

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### 6. Function with Return Value

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

result = add(10, 5)
print(result)  # Output: 15

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### 7. Positional vs Keyword Arguments

def student_info(name, age):
    print(f"Name: {name}, Age: {age}")

student_info("Ali", 22)  # Positional
student_info(age=22, name="Ali")  # Keyword

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### 8. Default Parameter Values

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

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

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### 9. Variable Number of Arguments

#### \*args – Multiple positional arguments:

def sum_all(*numbers):
    total = 0
    for num in numbers:
        total += num
    return total

print(sum_all(1, 2, 3, 4))  # Output: 10

#### \*\*kwargs – Multiple keyword arguments:

def print_details(**info):
    for key, value in info.items():
        print(f"{key}: {value}")

print_details(name="Ali", age=24, country="Egypt")

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### **10. Scope of Variables**

#### Local vs Global Variables

x = "global"

def func():
    x = "local"
    print(x)

func()     # Output: local
print(x)   # Output: global

Use global keyword if you want to modify a global variable inside a function.

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### 11. Docstrings (Function Documentation)

def square(n):
    """Returns the square of a number."""
    return n * n

print(square.__doc__)  # Output: Returns the square of a number.

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### 12. Best Practices

• Use descriptive names for functions
• Keep functions short and focused
• Avoid side effects unless needed
• Add docstrings for documentation

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### Exercise

• Create a function that takes a list and returns the average
• Create a function that takes any number of scores and returns the highest
• Create a function with default arguments for greeting a user by name and language

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#Python #Functions #CodingBasics #ModularProgramming #CodeReuse #PythonBeginners

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