Loops in Python (for & while)

A loop repeats a block of code so you don't have to copy-paste it. Python has two kinds. A for loop repeats over a sequence; a while loop repeats as long as a condition stays True:

# for loop: print numbers 1 to 5
for i in range(1, 6):
    print(i)

# while loop: count down from 3
n = 3
while n > 0:
    print(n)
    n -= 1

Let's understand each one.

The for loop

A for loop walks through each item in a sequence — a list, a string, or a range of numbers:

# Loop over a list of names
names = ["Asha", "Ravi", "Meena"]
for name in names:
    print(f"Hello, {name}")

# Loop over the characters of a string
for letter in "Python":
    print(letter)

To repeat a fixed number of times, use the built-in range():

# range(5) gives 0, 1, 2, 3, 4 — it stops BEFORE the end number
for i in range(5):
    print(i)

# range(start, stop, step)
for i in range(2, 11, 2):   # even numbers: 2, 4, 6, 8, 10
    print(i)

A key point about range(): it stops before the end value. range(1, 6) gives 1, 2, 3, 4, 5 — not 6.

The while loop

A while loop keeps running as long as its condition is True. Use it when you don't know in advance how many times you'll repeat:

# Keep asking until the user types "quit"
command = ""
while command != "quit":
    command = input("Enter a command (type 'quit' to stop): ")
    print(f"You said: {command}")

print("Goodbye!")

The danger here is the infinite loop: if the condition never becomes False, the loop never ends. Always make sure something inside the loop moves you toward stopping.

break and continue

Two keywords give you finer control:

• break exits the loop immediately.
• continue skips the rest of the current iteration and jumps to the next one.

# Stop at the first number divisible by 7
for n in range(1, 100):
    if n % 7 == 0:
        print(f"First multiple of 7 is {n}")
        break   # leave the loop now

# Print only odd numbers, skip the even ones
for n in range(1, 11):
    if n % 2 == 0:
        continue   # skip even numbers
    print(n)

Looping with an index using enumerate()

When you need both the item and its position, enumerate() is cleaner than tracking a counter yourself:

fruits = ["apple", "banana", "cherry"]

# enumerate gives (index, value) pairs
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")
# 0: apple
# 1: banana
# 2: cherry

A complete example

# Sum the numbers a user enters until they type 0

total = 0
while True:                      # loop forever...
    text = input("Enter a number (0 to finish): ")
    num = int(text)
    if num == 0:
        break                    # ...until we hit 0
    total += num                 # add to the running total

print(f"The total is {total}")

Common mistakes

• Infinite while loops: Forgetting to update the loop variable (e.g. missing n -= 1) means the condition never becomes False. If your program hangs, press Ctrl+C to stop it.
• Off-by-one with range: range(1, 5) gives 1, 2, 3, 4 — not 1 to 5. Remember it stops before the second number.
• Modifying a list while looping over it: Removing items from a list inside its own for loop can skip elements. Loop over a copy instead, or build a new list.
• Wrong indentation: Code that should be inside the loop must be indented under it. A line at the wrong indent level runs only once, after the loop.
• Using a while loop when for is clearer: If you're counting a known number of times, for i in range(n) is simpler and safer than a while with a manual counter.

FAQ

When should I use for vs while? Use for when you know the items or count (looping over a list, or a fixed range). Use while when you loop until some condition changes, like waiting for user input.

Can loops be nested? Yes. A loop inside a loop is common — for example, looping over rows and then columns of a grid. Each break or continue affects only its own loop.

What is else on a loop? A loop can have an else block that runs only if the loop finished without hitting break. It's an advanced feature you'll meet later.

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Loops pair naturally with collections. Read Lists in Python to see what you'll most often loop over, and If-Else Statements in Python for the conditions inside loops. Explore more on the Python learning hub.

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