Python Loops Explained – for Loop and while Loop with Examples and Output

Published on Code with Py | Category: Python Basics | Reading time: ~13 min

When learning Python, you will often need to repeat a task multiple times — printing numbers, processing a list, or checking user input again and again. Writing the same code repeatedly is not efficient. This is exactly where loops help. In this guide, you will learn what loops are, how the for loop and while loop work, when to use each one, and how they compare — with clear examples and outputs at every step.

What is a Loop in Python?
Types of Loops in Python
for Loop – Syntax and How it Works
for Loop Examples
When to Use a for Loop
while Loop – Syntax and How it Works
while Loop Examples
Infinite Loop and How to Avoid It
for Loop vs while Loop – Comparison
Real-Life Use Cases
Practice Problems
FAQ

1. What is a Loop in Python?

A loop is a programming construct that lets a block of code run repeatedly — either for a fixed number of times or until a certain condition becomes False. Without loops, you would have to write the same line of code again and again, which makes programs long, messy, and hard to maintain.

Here is what loops help you do:

Avoid repeating the same code multiple times
Reduce the length of your program significantly
Automate repetitive tasks like printing tables or processing lists
Build logic for real-world programs like ATMs, games, and forms

2. Types of Loops in Python

Python provides two main types of loops. Both can achieve the same results, but each is suited for different situations.

for loop

Used when iterations are known in advance
Works over sequences — lists, strings, ranges
Cleaner and more readable for fixed repetitions
Automatically stops at end of sequence

while loop

Used when iterations depend on a condition
Keeps running as long as condition is True
Best for user input, real-time checks
You must manually update the condition variable

3. for Loop – Syntax and How it Works

The for loop in Python iterates over items in a sequence one by one. For each item, it runs the code block inside the loop. When all items are exhausted, the loop stops automatically.

for variable in sequence:
    # code block to run for each item

The variable takes the value of each item in the sequence one at a time. The sequence can be a range(), a list, a string, a tuple, or any iterable.

4. for Loop Examples

Example 1 – Print numbers using range()

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

range(1, 6) generates the numbers 1, 2, 3, 4, 5. The stop value 6 is never included. The loop variable i takes each value automatically.

Example 2 – Iterate through a string

for ch in "Python":
    print(ch)

P
y
t
h
o
n

A string is a sequence of characters. The for loop picks each character one by one and runs the block for each one.

Example 3 – Loop through a list

fruits = ["Apple", "Banana", "Mango"]

for fruit in fruits:
    print(fruit)

Apple
Banana
Mango

Example 4 – Loop with index using enumerate()

Sometimes you need both the item and its position. Use enumerate() for this.

fruits = ["Apple", "Banana", "Mango"]

for index, fruit in enumerate(fruits):
    print(f"{index + 1}. {fruit}")

1. Apple
2. Banana
3. Mango

Example 5 – Sum of numbers using for loop

total = 0

for i in range(1, 11):
    total += i

print(f"Sum of 1 to 10: {total}")

Sum of 1 to 10: 55

Example 6 – Multiplication table

num = 5

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

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

5. When to Use a for Loop

Use for loop when:

Number of repetitions is known
Iterating over a list, string, or tuple
Using range() to count steps
Generating tables or sequences

Real-life examples:

Printing marks of each student
Displaying items in a shopping cart
Checking each character in a password
Printing a multiplication table

6. while Loop – Syntax and How it Works

The while loop keeps running a block of code as long as the condition is True. Unlike a for loop, it does not iterate over a sequence — it checks a condition before each iteration and stops only when that condition becomes False.

while condition:
    # code block runs as long as condition is True
    # update the condition variable here

Always update your condition variable inside the loop body. If you forget, the condition will never become False and the loop will run forever — this is called an infinite loop.

7. while Loop Examples

Example 1 – Print numbers 1 to 5

i = 1

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

The variable i starts at 1. After each iteration, i += 1 increases it by 1. When i becomes 6, the condition i <= 5 is False and the loop stops.

Example 2 – Countdown program

count = 5

while count > 0:
    print(count)
    count -= 1

print("Go!")

5
4
3
2
1
Go!

Example 3 – User input loop

This is one of the most practical uses of a while loop — keep asking the user for input until they type a specific value.

user_input = ""

while user_input != "exit":
    user_input = input("Type 'exit' to stop: ")
    print(f"You typed: {user_input}")

print("Loop ended.")

Type 'exit' to stop: hello
You typed: hello
Type 'exit' to stop: python
You typed: python
Type 'exit' to stop: exit
You typed: exit
Loop ended.

Example 4 – Sum of digits of a number

num = 1234
total = 0

while num > 0:
    total += num % 10
    num //= 10

print(f"Sum of digits: {total}")

Sum of digits: 10

This while loop extracts the last digit using % 10, adds it to total, then removes the last digit using // 10. It stops when no digits remain.

8. Infinite Loop and How to Avoid It

An infinite loop runs forever because its condition never becomes False. This can freeze or crash your program. Here is what one looks like:

while True:
    print("This runs forever!")

Never run an infinite loop without a break condition. To stop it manually in the terminal, press Ctrl + C. Always make sure your condition variable is updated inside the loop.

A controlled infinite loop with a break is acceptable and commonly used:

while True:
    answer = input("Enter 'quit' to exit: ")
    if answer == "quit":
        print("Goodbye!")
        break

Enter 'quit' to exit: hello
Enter 'quit' to exit: quit
Goodbye!

9. for Loop vs while Loop – Comparison

Feature	for Loop	while Loop
Best used when	Iterations are known in advance	Iterations depend on a condition
Iterates over	Sequences, ranges, lists, strings	A condition (True/False)
Stops automatically	Yes – when sequence ends	Only when condition is False
Risk of infinite loop	Very low	High if condition never changes
Counter variable	Managed by loop automatically	Must be updated manually
Readability	Cleaner for known repetitions	Cleaner for condition-based logic
Common use	Printing tables, iterating lists	User input, ATM PIN, game loop

10. Real-Life Use Cases

for loop real-life uses

Printing marks of all students in a class
Displaying items in a shopping cart
Sending emails to a contact list
Checking each character in a password
Generating OTP digits

while loop real-life uses

ATM asking for PIN until correct
Game running until player quits
Login page: allow 3 attempts
Downloading file until complete
Waiting for server response

11. Practice Problems

Try solving these on your own before searching for the answer. Understanding the logic is more important than getting the output immediately.

for loop problems

Print 1 to 10
Print all even numbers 1–20
Print each character of a string
Sum of numbers 1 to 100
Multiplication table of any number
Count vowels in a string
Print list items with index
Print 10 to 1 in reverse

while loop problems

Print 1 to 10 using while
Print 10 to 1 using while
Sum of digits of a number
Check if a number is palindrome
Reverse a given number
Ask user until they enter 0
Multiplication table using while
Login with 3 attempt limit

Write code yourself first. Test with at least 3 different inputs. If your output is wrong, trace through the loop manually — step by step — to find where the logic breaks.

Quick Summary – What You Learned

A loop repeats a block of code to avoid writing it multiple times
The for loop is best when the number of iterations is fixed
The while loop is best when iterations depend on a condition
range(start, stop, step) controls the for loop's counting
Always update the condition variable inside a while loop
An infinite loop runs forever — use break or fix the condition
Both loops can use break, continue, and else

Frequently Asked Questions (FAQ)

Q1. What is the main difference between a for loop and a while loop?

A for loop is used when the number of iterations is known in advance, such as looping through a list or a range. A while loop is used when the number of iterations depends on a condition that may change during execution.

Q2. Can a for loop replace a while loop in Python?

In most cases, yes — but it depends on the problem. For fixed repetitions and sequences, use for. For condition-based repetitions like user input or real-time checks, while is more natural and readable.

Q3. What is an infinite loop and how do I fix it?

An infinite loop runs forever because its condition never becomes False. Fix it by ensuring the condition variable is updated inside the loop body, or by adding a break statement when the goal is met.

Q4. Can I use a for loop without range() in Python?

Yes. You can loop directly over any iterable — a list, string, tuple, or dictionary. range() is just one way to generate a sequence of numbers for the loop to iterate over.

Q5. What happens if the while loop condition is False from the start?

The while loop body never executes even once. Python checks the condition before running the loop body, so if it is already False, the entire loop is skipped completely.

Q6. What is a nested loop in Python?

A nested loop is a loop placed inside another loop. The inner loop runs completely for each iteration of the outer loop. They are commonly used to work with 2D data like matrices or to print patterns.

Found this helpful? Share it with a friend who is learning Python. Drop your practice solutions in the comments — let's learn together!

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