Python For Loops

A for loop in Python iterates over every item in a sequence — a list, tuple, string, dictionary, set, or any other iterable — and executes a block of code once per item. Unlike languages where for typically counts numbers, Python's for is a for-each loop that walks through items directly.

This chapter covers:

• Basic syntax and how the loop variable works
• The range() function for counted loops
• break, continue, and the else clause
• enumerate() and zip() for richer iteration
• Iterating over strings, dictionaries, and nested structures
• Nested for loops
• The pass statement as a placeholder

Basic syntax

for variable in iterable:
    # block executed once per item

variable is assigned each successive item from iterable. The indented block runs once for every item.

Iterating over a list

Output:

apple
banana
cherry

The loop assigns "apple" to fruit, runs print(fruit), then moves on to "banana", and so on until all items are exhausted.

Iterating over a string

A string is itself an iterable — each character is an item:

for ch in "Python":
    print(ch)

Output:

P
y
t
h
o
n

The range() function

range() generates a sequence of integers on demand. It is the most common way to run a loop a specific number of times.

range(stop)
range(start, stop)
range(start, stop, step)

Counting from 1 to 5

Output:

1
2
3
4
5

range(1, 6) produces 1, 2, 3, 4, 5 — the stop value 6 is not included.

Counting in steps

for i in range(0, 10, 2):
    print(i)

Output:

0
2
4
6
8

Counting backwards

A negative step iterates in reverse:

for i in range(10, 0, -2):
    print(i)

Output:

10
8
6
4
2

The break statement

break exits the loop immediately, before all items have been visited.

for i in range(1, 6):
    if i == 3:
        break
    print(i)

Output:

1
2

Once i equals 3, break fires and the loop stops — 3, 4, and 5 are never printed.

When to use break: searching a list and stopping as soon as you find a match; exiting early from a long computation.

The continue statement

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

for i in range(1, 6):
    if i == 3:
        continue
    print(i)

Output:

1
2
4
5

When i equals 3, continue skips print(i) and jumps to i = 4.

The else clause

Python's for loop supports an optional else block that runs only if the loop completed normally (i.e., was not terminated by break).

for i in range(1, 4):
    print(i)
else:
    print("Loop finished")

Output:

1
2
3
Loop finished

If the loop exits via break, the else block is skipped:

for i in range(1, 6):
    if i == 3:
        break
    print(i)
else:
    print("Loop finished without break")

Output:

1
2

The else clause is useful for signalling whether a search succeeded — if you break on a match, the else block only runs when no match was found.

enumerate() — loop with index and value

enumerate() pairs each item with its position index, so you get both in one loop without a separate counter variable.

colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(index, color)

Output:

0 red
1 green
2 blue

To start counting from a different number, pass start:

fruits = ["apple", "banana", "cherry"]
for i, fruit in enumerate(fruits, start=1):
    print(i, fruit)

Output:

1 apple
2 banana
3 cherry

zip() — loop over two sequences at once

zip() pairs items from two (or more) iterables side by side:

names = ["Alice", "Bob", "Charlie"]
scores = [95, 87, 92]
for name, score in zip(names, scores):
    print(name, score)

Output:

Alice 95
Bob 87
Charlie 92

zip() stops when the shortest iterable is exhausted.

Iterating over dictionaries

Iterating over a dictionary by default yields its keys:

person = {"name": "Alice", "age": 30, "city": "Paris"}
for key in person:
    print(key, ":", person[key])

Output:

name : Alice
age : 30
city : Paris

Use .items() to get key-value pairs together:

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

Output:

name : Alice
age : 30
city : Paris

See also the Loop Dictionaries chapter for more patterns.

Nested for loops

A for loop can be placed inside another for loop. The inner loop runs fully for every single iteration of the outer loop.

Output:

red apple
red banana
red cherry
big apple
big banana
big cherry
tasty apple
tasty banana
tasty cherry

Gotcha: break inside a nested loop only exits the inner loop, not both. To exit both loops at once you need a flag variable or to refactor into a function and use return.

The pass statement

pass is a no-op placeholder. Use it when a for loop is syntactically required but you have nothing to put in the body yet:

for i in range(3):
    pass  # TODO: implement later

Without pass, Python would raise an IndentationError because an empty block is invalid syntax.

For loops vs list comprehensions

A common pattern is building a new list inside a for loop:

squares = []
for x in range(1, 6):
    squares.append(x ** 2)
print(squares)

Output: [1, 4, 9, 16, 25]

Python offers a more concise alternative called a list comprehension:

squares = [x ** 2 for x in range(1, 6)]
print(squares)

Output: [1, 4, 9, 16, 25]

List comprehensions are idiomatic for simple transformations; use a regular for loop when the body is complex or has side effects.

Choosing between for and while

Practice