DEV Community: vishwasenthil76

Lists in Python

vishwasenthil76 — Tue, 02 Jun 2026 16:53:59 +0000

A list is one of the most commonly used data structures in Python. It allows us to store multiple values in a single variable. Lists are flexible, easy to use, and help organize data efficiently.

What is a List?

A list is an ordered collection of items enclosed within square brackets []. The items can be of the same or different data types.

Example:
numbers = [10, 20, 30, 40, 50]

In this example, numbers is a list containing five integer values.

Features of Lists

Ordered

Lists maintain the order of elements as they are added.
fruits = ["Apple", "Banana", "Orange"]

Mutable

Lists can be modified after creation.
fruits[1] = "Mango"

Allow Duplicate Values
Lists can contain duplicate elements.
numbers = [1, 2, 2, 3, 3]
Store Different Data Types
A list can contain integers, strings, floats, and even other lists.
data = [10, "Python", 3.14, True]

Common List Operations

1.Adding Elements
numbers = [1, 2, 3]
numbers.append(4)

2.Removing Elements
numbers.remove(2)

3.Accessing Elements
print(numbers[0])

4.Finding Length
print(len(numbers))

5.Sorting a List
numbers.sort()

6.Reversing a List
numbers.reverse()

Applications of Lists

Storing student records
Managing employee details
Maintaining product inventories
Processing large datasets
Implementing stacks and queues

Advantages of Lists

Easy to create and use
Dynamic size
Supports various built-in methods
Can store multiple data types

List Indexing

Each element in a list has an index position starting from 0.

fruits = ["Apple", "Banana", "Orange"]
print(fruits[0])  # Apple

Negative Indexing

Python allows accessing elements from the end of the list using negative indexes.

print(fruits[-1])  # Orange

List Slicing

Slicing is used to extract a portion of a list.

numbers = [10, 20, 30, 40, 50]
print(numbers[1:4])  # [20, 30, 40]

Iterating Through a List

Lists can be traversed using loops.

for item in fruits:
    print(item)

Nested Lists

A list can contain another list.

matrix = [[1, 2], [3, 4], [5, 6]]

List Concatenation

Two or more lists can be combined using the '+' operator.

list1 = [1, 2]
list2 = [3, 4]
print(list1 + list2)

List Repetition

Lists can be repeated using the '*' operator.

numbers = [1, 2]
print(numbers * 3)

Membership Operators

We can check whether an element exists in a list.

fruits = ["Apple", "Banana", "Orange"]
print("Apple" in fruits)

List Comprehension

A concise way to create lists.

squares = [x*x for x in range(1, 6)]
print(squares)

Built-in Functions Used with Lists

len() – Returns the number of elements.
max() – Returns the largest element.
min() – Returns the smallest element.
sum() – Returns the sum of all elements.
sorted() – Returns a sorted list.

Key Takeaways

Lists are ordered and mutable.
Lists support indexing and slicing.
Lists can store multiple data types.
Lists provide many built-in methods for data manipulation.
Lists are one of the most frequently used data structures in Python.

Functions in python

vishwasenthil76 — Fri, 29 May 2026 17:32:29 +0000

What is a Function in Python?

A function is a block of code designed to perform a particular task.
We use the def keyword to create a function.

Syntax
def function_name():

Example

def welcome():
    print("Welcome to Python")

Calling the function:

welcome()

Output
Welcome to Python

Types of Functions in Python

Function Without Parameters

These functions do not take any input values.

Example

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

greet()

Explanation
greet() function is created
No parameters are passed
The function simply prints a message

Function With Parameters

Parameters allow us to send values into a function.

Example

def greet(name):
    print("Hello", name)

greet("Vishwa")

Output
Hello Vishwa

Explanation
name is the parameter
"Vishwa" is the argument passed to the function

Function With Return Value

Functions can return results using the return keyword.

Example

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

result = add(5, 3)

print("Sum is:", result)

Output
Sum is: 8

Explanation
The function calculates the sum
return sends the result back to the caller

Function With Default Parameter

Default parameters are used when no value is passed.

Example

def greet(name="Guest"):
    print("Hello", name)

greet("Vishwa")
greet()

Output
Hello Vishwa
Hello Guest

Explanation
If no argument is passed, "Guest" becomes the default value

Function With Variable Length Arguments

Sometimes we do not know how many inputs will be passed.
Python uses *args for this.

Example

def numbers(*args):
    total = 0

    for num in args:
        total += num

    print("Sum is:", total)

numbers(1, 2, 3, 4, 5)

Output
Sum is: 15
Explanation

*args stores all values as a tuple
The loop adds all numbers
Local Variable and Global Variable
Local Variable

A variable created inside a function is called a local variable.

Example

def sample():
    x = 10
    print(x)

sample()

x can only be used inside the function.

Global Variable

A variable created outside the function is called a global variable.

Example

x = 100

def sample():
    print(x)

sample()

Explanation
Global variables can be accessed anywhere in the program
Real-Time Example: Student Mark Analysis

Functions can also be used in real-world problems like student record processing.

CRACKING CODING INTERVIEW

vishwasenthil76 — Sun, 24 May 2026 06:25:56 +0000

Technical Interview

Technical interviews are an important part of the hiring process in many technology companies. These interviews are designed not only to test coding ability but also to evaluate problem-solving skills, communication, and technical knowledge. Understanding how interviewers assess candidates helps students prepare effectively.

A) Role of Algorithm & Coding Questions

Algorithms form major part of interviews
Interview focuses on problem solving
Sometimes only one problem is discussed in an interview because time is limited (around 45 minutes)

B) Skills Evaluated by Interviewers

Analytical Skills

Problem solving ability
Solution optimization
Decision making

Coding Skills

Writing clean code
Error handling
Code organization

Technical Knowledge

Data structures
Algorithms
CS fundamentals

Experience

Projects
Technical decisions
Initiative

Communication & Culture Fit

Communication is important because employees work in teams.
Interviewers observe:

Confidence
Communication style
Teamwork
Personality fit with company culture

Evaluation is based on Ability to convert logic into code.

Interviewers observe:

Clean code writing
Proper formatting
Error handling
Readability

for Example:

Bad code:

a=[1,2,3]
for i in a:print(i)

Good code:

numbers = [1,2,3]

for num in numbers:
    print(num)

C) Why Companies Use This Process?

Problem-solving skills are valuable

Companies believe candidates who solve difficult problems can contribute effectively.

Data structures & algorithms knowledge

Topics like:

Trees
Graphs
Lists
Sorting

are considered important foundations.

Whiteboard Interviews

Focus on logic instead of syntax
Encourages communication
Tests thinking process

Interviewers do not expect perfect syntax. They observe how candidates approach solutions.

D) Interview Question Selection

No fixed question list in most companies
Interviewers choose questions individually
Questions are often similar across companies like Google, Amazon, and Meta

E) Candidate Evaluation System

Candidates are assessed by comparing performance with previous candidates who solved the same question rather than using fixed marks. Hard questions are difficult for everyone, so receiving a difficult problem does not necessarily reduce chances of success.
Candidate Evaluation Process

There is usually no strict marking scheme.

Interviewers compare candidates based on:

Speed
Solution quality
Hints required
Alternative approaches
Communication

Example:

Candidate A → solved in 10 mins independently
Candidate B → solved in 20 mins with hints

Looping Concept

vishwasenthil76 — Fri, 22 May 2026 12:50:17 +0000

In python, loops are mainly used to execute a block of code repeatedly.
There are two main types of loop:
1.While loop
2.For loop

1. While Loop

A while loop runs as long as the condition is true.

Example:

i = 1

while i <= 5:
    print(i)
    i += 1

Output:

1
2
3
4
5

flowchart of While loop:

2. For Loop

A for loop is used to repeat a block of code for every item in a sequence such as a string, list, or range.

Using For Loop with String

Example:

name = "Python"

for ch in name:
    print(ch)

Output:

P
y
t
h
o
n

flowchart of For loop:

Linear Search

In Linear Search, we iterate over all the elements of the array and check if it the current element is equal to the target element. If we find any element to be equal to the target element, then return the index of the current element. Otherwise, if no element is equal to the target element, then return -1 as the element is not found.
Linear search is also known as sequential search.

Time Complexity of Linear search:
->Best case: O(1)
->Average case: O(N)
->Worst case: O(N)

Flowchart of Linear search:

Binary search

Binary search works only on sorted data. Instead of checking every element one by one, it checks the middle element and decides whether to search on the left side or right side.
This method reduces the number of comparisons and makes searching faster.

Time Complexity of Binary search:
-> Best Case: O(1)
-> Average Case: O(log N)
-> Worst Case: O(log N)

Flowchart of Binary search:

references:
https://www.geeksforgeeks.org/python/loops-in-python/
https://www.geeksforgeeks.org/dsa/linear-search/