Length and iteration methods in Python

Introduction

We use length and iteration methods to count items and go through each item in a list or other collection. This helps us work with groups of things easily.

When you want to know how many items are in a list or string.

When you want to do something with each item in a list, like print or change it.

When you want to check if a collection is empty or not.

When you want to add up or find something from all items in a collection.

When you want to repeat an action a certain number of times.

Syntax

Python

len(collection)

for item in collection:
    # do something with item

len() gives the number of items in a collection like list, string, or tuple.

The for loop goes through each item one by one.

Examples

This prints the number of items in the list numbers, which is 4.

Python

numbers = [1, 2, 3, 4]
print(len(numbers))

This prints the number of letters in the word "hello", which is 5.

Python

word = "hello"
print(len(word))

This prints each fruit name on its own line by going through the list.

Python

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

This repeats the loop 3 times, printing numbers 0, 1, and 2.

Python

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

Sample Program

This program counts how many items are in the list and prints each item one by one.

Python

items = ["pen", "book", "lamp"]
print(f"There are {len(items)} items.")

for item in items:
    print(f"Item: {item}")

Important Notes

You can use len() on many types like lists, strings, tuples, and dictionaries.

The for loop works with any collection that can be counted or listed.

Indentation is important in Python to show what is inside the loop.

Summary

len() tells you how many items are in a collection.

for loops let you do something with each item in a collection.

These tools help you handle groups of things easily and clearly.