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Fibonacci numbers are part of a famous sequence where each number is the sum of the two preceding ones, i.e. F(n) = F(n-1) + F(n-2). The sequence starts as:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Notice that every number is equal to the sum of its previous 2 numbers.

In this article, we will learn how to identify if a given number belongs to the Fibonacci series or not.

Examples : 

Input: 8 Output: Yes Input: 31 Output: No

Fibonacci Number Check Using a Mathematical Property

A number n is a Fibonacci number if and only if one or both of (5*n² + 4) or (5*n² – 4) is a perfect square.

The above mathematical expression is derived from the closed-form expression of Fibonacci numbers (Binet’s Formula) and some number theory. It’s fast and doesn’t require generating the Fibonacci sequence. Let's look at the code implementation in Python:import math​def is_perfect_sq(x): s = int(math.sqrt(x)) return s * s == x​def is_fibonacci(n): return is_perfect_sq(5 * n * n + 4) or is_perfect_sq(5 * n * n - 4)​for i in range(1, 7): if is_fibonacci(i): print(f"{i} is a Fibonacci Number") else: print(f"{i} is not a Fibonacci Number")

Output1 is a Fibonacci Number 2 is a Fibonacci Number 3 is a Fibonacci Number 4 is not a Fibonacci Number 5 is a Fibonacci Number 6 is not a Fibonacci Number

Explanation:

1. is_perfect_sq(x):

Calculates the integer square root of x.

Returns True if x is a perfect square, else False.

2. is_fibonacci(n):

Applies the mathematical identity:

A number n is Fibonacci if 5*n² + 4 or 5*n² – 4 is a perfect square.

Calls is_perfect_sq() on both expressions to check this.

Random numbers play a crucial role in programming and real-world applications such as games, simulations, cryptography, data science, testing, and machine learning. Python makes working with random numbers simple and efficient through its built-in random module.

If you are new to Python, you might wonder: What is a random number generator in Python, and how do we use it?

This article explains the concept of random number generation, how Python generates random numbers, and how to use different random functions with clear examples.

What Is a Random Number Generator?

A Random Number Generator (RNG) is a system that generates a sequence of numbers that appear to be random.

In Python:

Random numbers are pseudo-random, not truly random

They are generated using mathematical algorithms

The sequence can be reproduced using a seed value

In simple terms:

Python’s random number generator produces values that behave like random numbers for practical use.

Random Number Generator in Python

Python provides the random module to generate random numbers and perform random operations.

Importing the random Module

import random

Once imported, you can access various random functions.

Generating Random Integers

The most commonly used function is randint().

Syntax

random.randint(start, end)

Example

import random num = random.randint(1, 10) print(num)

✔ Generates a random integer between 1 and 10 (inclusive).

Generating Random Floating-Point Numbers

Use random() to generate random float values.

Example

import random value = random.random() print(value)

✔ Generates a float value between 0.0 and 1.0.

Generating Random Float in a Range

Use uniform() to generate a float within a specific range.

Example

import random value = random.uniform(10, 20) print(value)

✔ Generates a float between 10 and 20.

Selecting Random Elements

Using choice()

import random colors = ["red", "blue", "green", "yellow"] print(random.choice(colors))

✔ Randomly selects one element from a list.

Generating Multiple Random Values

Using sample()

import random numbers = [1, 2, 3, 4, 5] print(random.sample(numbers, 3))

✔ Selects 3 unique random elements.

Shuffling Elements Randomly

Using shuffle()

import random cards = [1, 2, 3, 4, 5] random.shuffle(cards) print(cards)

✔ Randomly rearranges elements in a list.

Using Random Seed

A seed controls the randomness sequence.

Example

import random random.seed(10) print(random.randint(1, 100))

✔ Same seed → same output ✔ Useful for testing and debugging

Random Number Generator Functions Summary

FunctionDescriptionrandom()Random float (0.0 to 1.0)randint(a, b)Random integeruniform(a, b)Random floatchoice(seq)Random elementsample(seq, k)Random sampleshuffle(seq)Shuffle sequenceseed(x)Set randomness

Real-World Applications of Random Numbers

Python RNG is used in:

Games and simulations

Password generation

Data sampling

Machine learning

Testing and automation

Statistical modeling

Is Python’s Random Generator Truly Random?

No. Python uses pseudo-random algorithms, which means:

Results look random

Sequence can be reproduced

Suitable for most applications

For cryptographic security, Python provides the secrets module.

Common Beginner Mistakes

Forgetting to import the random module

Confusing randint() and random()

Expecting true randomness

Using random for security purposes

Random Number Generator Interview Questions

What is a random number generator?

How does Python generate random numbers?

Difference between randint() and random()?

What is a seed in Python?

Is Python RNG secure?

Best Practices

Use random for general purposes

Use secrets for security-related tasks

Set seeds for reproducible results

Avoid relying on randomness for critical logic

The Random Number Generator in Python allows developers to generate numbers and values that simulate randomness for a wide range of applications. Using the built-in random module, you can generate integers, floats, random elements, shuffled lists, and reproducible results with ease.

Loops are a fundamental concept in programming that allow you to execute a block of code repeatedly. In Python, the for loop is one of the most commonly used loops because it is simple, readable, and powerful.

Whether you are a beginner learning Python or preparing for coding interviews, understanding the Python for loop is essential. This tutorial explains the syntax, working, examples, and practice problems to help you master the for loop in Python.

What Is a For Loop in Python?

A for loop in Python is used to iterate over a sequence such as:

List

Tuple

String

Dictionary

Set

Range

In simple words:

A for loop repeats a block of code for each element in a sequence.

Syntax of Python For Loop

for variable in sequence: statements

variable → Takes the value of each element

sequence → Collection or range

statements → Code executed in each iteration

Basic Example of For Loop

for i in range(5): print(i)

Output

0 1 2 3 4

How Python For Loop Works

The loop picks the first element from the sequence

Executes the block of code

Moves to the next element

Repeats until the sequence ends

For Loop Using range()

The range() function is commonly used with for loops.

Example

for i in range(1, 6): print(i)

Output

1 2 3 4 5

For Loop With List

languages = ["Python", "Java", "C++"] for lang in languages: print(lang)

Output

Python Java C++

For Loop With String

for ch in "Python": print(ch)

Output

P y t h o n

For Loop With Tuple

numbers = (10, 20, 30) for n in numbers: print(n)

For Loop With Dictionary

student = {"name": "Alice", "age": 21} for key, value in student.items(): print(key, value)

Nested For Loop

A nested for loop means a loop inside another loop.

Example

for i in range(1, 4): for j in range(1, 3): print(i, j)

Output

1 1 1 2 2 1 2 2 3 1 3 2

For Loop With break

The break statement stops the loop immediately.

for i in range(1, 6): if i == 4: break print(i)

For Loop With continue

The continue statement skips the current iteration.

for i in range(1, 6): if i == 3: continue print(i)

For Loop With else

The else block executes after the loop finishes normally.

for i in range(3): print(i) else: print("Loop completed")

Practice Examples for Python For Loop

1. Print Numbers From 1 to 10

for i in range(1, 11): print(i)

2. Find Sum of Numbers

total = 0 for i in range(1, 6): total += i print(total)

3. Print Even Numbers

for i in range(1, 21): if i % 2 == 0: print(i)

4. Multiplication Table

num = 5 for i in range(1, 11): print(num, "x", i, "=", num * i)

5. Count Characters in a String

count = 0 for ch in "Python": count += 1 print(count)

Common Beginner Mistakes

Forgetting indentation

Using wrong range values

Confusing for with while

Modifying the sequence inside loop

Time Complexity of For Loop

The time complexity depends on:

Number of iterations

Operations inside the loop

Usually:

O(n) for simple loops

For Loop Interview Questions

What is a for loop in Python?

Difference between for loop and while loop?

What is range()?

Can for loop be used with else?

Difference between break and continue?

When to Use For Loop

Iterating over sequences

Repeating tasks fixed number of times

Processing data collections

Writing clean and readable code

The Python for loop is one of the most powerful and beginner-friendly looping constructs. It helps you iterate over data efficiently, write clean code, and solve real-world programming problems.