for

Updated March 16, 2026 · Keywords

keyword loop iteration control-flow

The for keyword iterates over sequences in Python. It’s the primary way to loop through collections, strings, ranges, and other iterables.

Syntax

for variable in iterable:
    # Loop body

Basic Examples

Iterating Over a List

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

for fruit in fruits:
    print(fruit)
# apple
# banana
# cherry

Iterating Over a String

for char in "Python":
    print(char)
# P
# y
# t
# h
# o
# n

Using range()

for i in range(5):
    print(i)
# 0
# 1
# 2
# 3
# 4

Using the Index

enumerate()

Get both index and value:

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

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

Starting Index

for index, fruit in enumerate(fruits, start=1):
    print(f"{index}: {fruit}")
# 1: apple
# 2: banana
# 3: cherry

Iterating Over Dictionaries

Keys Only

person = {"name": "Alice", "age": 30, "city": "NYC"}

for key in person:
    print(key)
# name
# age
# city

Key-Value Pairs

for key, value in person.items():
    print(f"{key}: {value}")
# name: Alice
# age: 30
# city: NYC

The else Clause

Runs after the loop completes normally:

for i in range(3):
    print(i)
else:
    print("Loop completed!")
# 0
# 1
# 2
# Loop completed!

The else block doesn’t run if you break out of the loop:

for i in range(5):
    if i == 3:
        break
    print(i)
else:
    print("Loop completed!")
# 0
# 1
# 2

Nested Loops

matrix = [[1, 2], [3, 4], [5, 6]]

for row in matrix:
    for num in row:
        print(num, end=" ")
    print()
# 1 2
# 3 4
# 5 6

List Comprehension Alternative

For simple transformations, consider list comprehensions:

# Traditional loop
squares = []
for i in range(5):
    squares.append(i ** 2)

# List comprehension
squares = [i ** 2 for i in range(5)]

Breaking and Continuing

break - Exit Loop Early

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

for fruit in fruits:
    if fruit == "cherry":
        break
    print(fruit)
# apple
# banana

continue - Skip Current Iteration

for i in range(5):
    if i == 2:
        continue
    print(i)
# 0
# 1
# 3
# 4

Best Practices

Use enumerate Instead of range(len())

# Avoid
for i in range(len(fruits)):
    print(fruits[i])

# Prefer
for fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

Choose the Right Iteration Method

Task	Use
Process each item	`for item in iterable`
Need index and value	`enumerate()`
Key-value pairs	`.items()`
Fixed count	`range(n)`

Keep Loops Simple

Extract complex logic into helper functions:

# Avoid deeply nested loops
# Extract logic into functions when possible

Common Patterns

Finding an Item

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

for fruit in fruits:
    if fruit.startswith("b"):
        print(f"Found: {fruit}")
        break
# Found: banana

Aggregating Values

numbers = [1, 2, 3, 4, 5]
total = 0

for num in numbers:
    total += num

print(total)
# 15

Filtering Items

numbers = [1, 2, 3, 4, 5, 6]
evens = []

for num in numbers:
    if num % 2 == 0:
        evens.append(num)

print(evens)
# [2, 4, 6]