For Loops

A for loop lets you repeat a block of code for every item in a sequence. Instead of writing the same thing over and over, you write it once and tell Python to run it for each item.

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

for fruit in fruits:
    print(fruit)

Output:

apple
banana
mango

Python takes the list, picks each item one by one, puts it in fruit, runs the block, then moves to the next item. When there are no items left, the loop ends.

How it works

The loop always asks — is there a next item? If yes, run the block. If no, stop.

Looping over different sequences

A for loop works on anything Python can iterate over — not just lists.

String — loops over each character:

name = "Ali"

for letter in name:
    print(letter)

Output:

A
l
i

Tuple:

colors = ("red", "green", "blue")

for color in colors:
    print(color)

Dictionary — loops over keys by default:

person = {"name": "Ali", "age": 22, "city": "Lahore"}

for key in person:
    print(key)

Output:

name
age
city

To get both key and value, use .items():

for key, value in person.items():
    print(f"{key}: {value}")

Output:

name: Ali
age: 22
city: Lahore

range() — looping over numbers

range() generates a sequence of numbers. You do not need a list — just tell it where to start, where to stop, and how to step.

Basic — count from 0 to 4:

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

Output:

range(5) gives you 0, 1, 2, 3, 4 — it stops before 5, never including it.

Start and stop:

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

Output:

Start, stop, and step:

for i in range(0, 20, 5):
    print(i)

Output:

Counting backwards:

for i in range(5, 0, -1):
    print(i)

Output:

range(stop) — starts at 0, stops before stop

range(start, stop) — starts at start, stops before stop

range(start, stop, step) — same but jumps by step each time

enumerate() — loop with an index

Sometimes you need both the item and its position. enumerate() gives you both:

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

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

Output:

0: apple
1: banana
2: mango

You can start the index from any number:

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

Output:

1. apple
2. banana
3. mango

Without enumerate(), people often do this — which works but is not Pythonic:

for i in range(len(fruits)):
    print(f"{i}: {fruits[i]}")

Use enumerate() instead. It is cleaner and easier to read.

zip() — loop over two sequences together

zip() lets you loop over two sequences at the same time, pairing items by position:

names = ["Ali", "Sara", "Omar"]
scores = [88, 95, 72]

for name, score in zip(names, scores):
    print(f"{name} scored {score}")

Output:

Ali scored 88
Sara scored 95
Omar scored 72

If one sequence is shorter, zip() stops at the shorter one:

names = ["Ali", "Sara", "Omar"]
scores = [88, 95]

for name, score in zip(names, scores):
    print(f"{name}: {score}")

Output:

Ali: 88
Sara: 95

Omar has no matching score so Python stops there.

Nested for loops

A loop inside a loop. The inner loop runs completely for every single iteration of the outer loop.

rows = 3
cols = 3

for row in range(1, rows + 1):
    for col in range(1, cols + 1):
        print(f"({row},{col})", end=" ")
    print()

Output:

(1,1) (1,2) (1,3)
(2,1) (2,2) (2,3)
(3,1) (3,2) (3,3)

A classic use — multiplication table:

for i in range(1, 6):
    for j in range(1, 6):
        print(f"{i * j:3}", end="")
    print()

Output:

  1  2  3  4  5
  2  4  6  8 10
  3  6  9 12 15
  4  8 12 16 20
  5 10 15 20 25

Be careful with deep nesting. Two levels is usually fine. Three or more levels makes code very hard to read — consider breaking it into functions instead.

A real example

Calculate the total and average score for a student:

name = "Ali"
scores = [88, 92, 79, 95, 84]
total = 0

for score in scores:
    total += score

average = total / len(scores)

print(f"Student: {name}")
print(f"Total: {total}")
print(f"Average: {average:.1f}")

Output:

Student: Ali
Total: 438
Average: 87.6

Summary

Concept	Example
Loop over a list	`for item in list:`
Loop N times	`for i in range(N):`
Loop with index	`for i, item in enumerate(list):`
Loop two lists together	`for a, b in zip(list1, list2):`
Loop dict key + value	`for k, v in dict.items():`

For Loops

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