for Loops

A for loop iterates over a sequence — such as a list, tuple, set, dictionary, or string — and executes a block of code once for each item.

for city in ["Delhi", "Mumbai"]:
    print(city)

Unlike the traditional for loop in languages such as C or Java, which counts with an index (for (i = 0; i < n; i++)), Python's for loop works like an iterator: it automatically moves through each item without requiring you to manage an index variable.

Syntax

for variable in iterable:
    # code to run for each item

Part	Meaning
variable	A name that receives the current item on each iteration
iterable	Any object you can loop over: a list, tuple, string, set, dictionary, range, file, and more
Indented block	The code that runs once per item

Basic for Loop Example

Example: Looping Through a List

cities = ["Delhi", "Mumbai", "Chennai"]

for city in cities:
    print(city)

Expected output:

Delhi
Mumbai
Chennai

How it works:

1. On the first iteration, Python assigns "Delhi" to city and runs the block.
2. On the second iteration, city becomes "Mumbai".
3. On the third iteration, city becomes "Chennai".
4. There are no items left, so the loop ends.

Note: You do not need to create or update an index variable — Python handles the iteration for you. This makes for loops shorter and less error-prone than index-based while loops.

Practical Example: Calculating a Total

prices = [250, 120, 80]
total = 0

for price in prices:
    total += price

print("Total:", total)

Expected output:

Total: 450

total starts at 0, and each iteration adds the current price to it. This accumulator pattern is one of the most common uses of loops.

Looping Through a String

Strings are iterable, so a for loop can visit each character in order.

Example: Iterating Over Characters

word = "Python"

for letter in word:
    print(letter)

Expected output:

P
y
t
h
o
n

The break Statement

break stops the loop immediately, even if items remain.

Example: Stop When a Condition Is Met

numbers = [10, 20, 30, 40, 50]

for n in numbers:
    if n == 30:
        break
    print(n)

Expected output:

10
20

The loop exits as soon as 30 is reached. Because break comes before print(n), 30 itself is never printed.

break After Output

The position of break matters. If you print first and then check, the matching item is displayed:

colors = ["red", "green", "blue"]

for color in colors:
    print(color)
    if color == "green":
        break

Expected output:

red
green

Compare it with break placed before the output:

colors = ["red", "green", "blue"]

for color in colors:
    if color == "green":
        break
    print(color)

Expected output:

red

The continue Statement

continue skips the rest of the current iteration and moves on to the next item.

Example: Skip a Specific Value

animals = ["dog", "cat", "cow", "horse"]

for animal in animals:
    if animal == "cat":
        continue
    print(animal)

Expected output:

dog
cow
horse

When animal is "cat", continue skips the print(); the loop then carries on with "cow".

Statement	Effect
break	Exits the entire loop
continue	Skips to the next item

The range() Function

To repeat a block a specific number of times, loop over range(). It generates a sequence of integers.

Basic range()

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

Expected output:

0
1
2
3
4

range(5) produces five numbers, starting at 0 and stopping before 5.

range() With a Start Value

for i in range(3, 8):
    print(i)

Expected output:

3
4
5
6
7

The sequence starts at 3 (included) and stops before 8 (excluded).

range() With a Step Value

The third argument sets the step — how much to add each time.

for i in range(2, 20, 4):
    print(i)

Expected output:

2
6
10
14
18

A negative step counts down:

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

Expected output:

5
4
3
2
1

Form	Generates
range(stop)	0 up to stop - 1
range(start, stop)	start up to stop - 1
range(start, stop, step)	start, start + step, … while before stop

range() is covered in more detail in the Python Range lesson.

Getting the Index With enumerate()

When you need both the position and the item, use enumerate():

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

for index, fruit in enumerate(fruits):
    print(index, fruit)

Expected output:

0 mango
1 apple
2 kiwi

enumerate() produces (index, item) pairs, which are unpacked into the two loop variables. Pass a second argument to start counting from a different number, for example enumerate(fruits, 1).

The else Block With a for Loop

A for loop can have an else block. It runs only if the loop completes normally, without hitting break.

Example: Loop Completion

for i in range(4):
    print(i)
else:
    print("Loop completed successfully")

Expected output:

0
1
2
3
Loop completed successfully

else Is Skipped When break Is Used

for i in range(6):
    if i == 4:
        break
    print(i)
else:
    print("This will not be printed")

Expected output:

0
1
2
3

The loop ends with break, so the else block is skipped.

Practical Use: Searching for an Item

usernames = ["asha", "ravi", "meena"]
search = "john"

for name in usernames:
    if name == search:
        print("User found")
        break
else:
    print("User not found")

Expected output:

User not found

The else block runs only when the loop checked every name without finding a match. Think of it as "no break occurred".

Nested for Loops

A nested loop is a loop inside another loop. The inner loop runs completely for each iteration of the outer loop.

Example: Combining Two Lists

sizes = ["small", "medium"]
items = ["shirt", "jacket"]

for size in sizes:
    for item in items:
        print(size, item)

Expected output:

small shirt
small jacket
medium shirt
medium jacket

How it works:

1. The outer loop takes size = "small".
2. The inner loop runs fully: "shirt", then "jacket".
3. The outer loop moves to size = "medium", and the inner loop runs fully again.

With 2 sizes and 2 items, the inner print() runs 2 × 2 = 4 times.

Example: Multiplication Table

for row in range(1, 4):
    for col in range(1, 4):
        print(row * col, end="\t")
    print()

Expected output (columns separated by tabs):

1	2	3
2	4	6
3	6	9

• end="\t" prints a tab instead of a newline, keeping each row on one line.
• The empty print() after the inner loop moves to the next line.

Note: break and continue affect only the innermost loop they are in.

The pass Statement in Loops

A for loop body cannot be empty. If you need the loop structure but have no logic yet, use pass:

for i in range(3):
    pass

This loop runs three times and does nothing, but it prevents a syntax error.

Looping Through Other Collections

# Tuple
for n in (1, 2, 3):
    print(n, end=" ")
print()

# Dictionary (keys and values)
stock = {"pen": 10, "book": 4}
for item, quantity in stock.items():
    print(item, quantity)

Expected output:

1 2 3 
pen 10
book 4

Common Mistakes

Mistake	Problem
Forgetting the colon	SyntaxError: expected ':'
Expecting range(5) to include 5	range stops before the stop value
Modifying a list while looping over it	Items may be skipped; loop over a copy (items[:]) instead
Using range(len(items)) when only items are needed	Works, but for item in items is cleaner
Misplacing break before or after output	Changes whether the matching item is printed

Related Concepts

• Python while Loops — loops controlled by a condition
• Python Range — generating number sequences
• Python Iterators — how for loops work internally
• Python Lists, Tuples, Sets, and Dictionaries — common iterables