Python Loops: for & while - Day - 4

What Is a Loop? 🤔

A loop tells Python: keep doing this thing, again and again, until I say stop. Without loops, repetitive tasks mean writing the same line over and over. With loops, you write it once and Python handles all the repetitions automatically.

Imagine you want to say “Good Morning” to 5 friends. You could write five separate print statements. Now imagine 100 friends - would you really write 100 lines? That would be exhausting. That is exactly where loops save you.

# ❌ Without a loop - exhausting, doesn't scale
print("Good Morning, Priya!")
print("Good Morning, Rahul!")
print("Good Morning, Meena!")
print("Good Morning, Arjun!")
print("Good Morning, Sneha!")
# Imagine 100 of these... 😅

Python gives you two types of loops - each for a different situation:

• for loop - when you know how many times to repeat, or what to loop over
• while loop - when you want to keep going until a condition is met

The for Loop 🔁

Think of a for loop like going through a list one by one - like checking your grocery list item by item. Python picks each value, runs your code block with it, then moves to the next.

Basic Syntax

for item in collection:
    # do something with item
    # runs once for each value in the collection

Printing Numbers from a List

for number in [1, 2, 3, 4, 5]:
    print(number)

# Output:
# 1
# 2
# 3
# 4
# 5

Python picked each number from the list one by one and ran print() for each. That is it - simple as that.

Example 1 - Print Names from a List

friends = ["Priya", "Rahul", "Meena"]

for name in friends:
    print("Good Morning,", name)

# Output:
# Good Morning, Priya
# Good Morning, Rahul
# Good Morning, Meena

Using range()

Writing a list manually every time is boring. That is why Python has a built-in function called range(). It creates a sequence of numbers for you automatically - no need to type them all out.

range(5)          # 0, 1, 2, 3, 4   - starts at 0, stops before 5
range(2, 6)       # 2, 3, 4, 5      - starts at 2, stops before 6
range(1, 10, 2)   # 1, 3, 5, 7, 9   - step of 2

# Think of it as: range(start, stop, step)
# Start from where? Stop before where? Jump by how much?

Example 2 - Say Hello 5 Times

for i in range(5):
    print("Hello!")

# Output: Hello! (printed 5 times)

Example 3 - Sum of Numbers

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

print("Total:", total)   # Total: 15

Example 4 - Multiplication Table

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

# Output:
# 5 x 1 = 5
# 5 x 2 = 10
# ...and so on up to 5 x 10 = 50

The while Loop ⏳

A while loop keeps running as long as a condition is True. The moment the condition becomes False, it stops. Think of it like a traffic light - keep waiting while the light is red. When it turns green, go!

Basic Syntax

while condition:
    # do something
    # make sure something changes so condition eventually becomes False!

Example 1 - Count from 1 to 5

count = 1

while count <= 5:
    print(count)
    count = count + 1   # ← CRITICAL: update count or loop runs forever

# Output: 1  2  3  4  5

Example 2 - Guess the Number

secret = 7
guess  = 0

while guess != secret:
    guess = int(input("Guess the number: "))

    if guess == secret:
        print("You got it! 🎉")
    else:
        print("Try again!")

# Loop keeps running until guess == secret
# Once correct, guess != secret becomes False → loop ends

This is the classic while use case - when you don’t know in advance how many attempts it will take. You couldn’t do this cleanly with a for loop because you don’t know the count ahead of time.

Infinite Loops ♾️

If the condition in a while loop never becomes False, your loop runs forever - your program gets stuck, your terminal freezes, your CPU hits 100%. Every beginner creates one eventually. Here is how to deal with it.

# ❌ Infinite loop - count never changes!
count = 1
while count <= 5:
    print(count)
    # forgot count += 1 → runs forever

# ✓ while True - intentional infinite loop with a break
while True:
    answer = input("Type 'quit' to exit: ")
    if answer == "quit":
        break   # ← this is the intentional exit point
    print(f"You typed: {answer}")

Bonus: break and continue

Two small keywords that give you fine-grained control over loop execution. You will use both of these constantly in real Python code.

As soon as i becomes 5, break exits the loop completely - 5, 6, 7… are never printed. With continue, when i is 3, Python skips the print and goes straight to the next round - so 3 is never printed but the loop continues.

for vs while - Which One to Use?

One of the most common questions on Day 4. The answer is simpler than you think - there is a clear mental test that gives you the right answer almost every time.

Your Turn - 4 Exercises

Try these exercises to make sure everything clicked. Don’t just read - actually type the code. Even if you make mistakes, that is how you learn Python the fastest!

1. Print all even numbers from 1 to 20 using a for loop
2. Use a while loop to keep asking someone to enter a password until they type the correct one
3. Print a countdown from 10 to 1 using range(), then print “Go! 🚀”
4. Loop through a list of your favourite movies and print each one with its number (1. Movie, 2. Movie…)

Loops are what make programs actually useful.

You can now process any list, repeat any action, and automate any repetitive task. From reading files to processing data to building automation scripts - loops are everywhere in real Python. Keep coding! 🚀