Is the Lists & Looping lesson free?

Yes. The first 5 lessons on PyRun are free forever — no signup, no card. Lists & Looping runs real Python in your browser via Pyodide.

How long does the Lists & Looping lesson take?

About 6 minutes end-to-end. It's a hands-on lesson — you read a paragraph, edit the code, and run it in the same tab.

Do I need to install Python to try the Lists & Looping lesson?

No install required. PyRun runs real CPython in your browser via Pyodide (Python compiled to WebAssembly). Works on Chrome, Firefox, Safari, and Edge — desktop or mobile.

What level is the Lists & Looping lesson?

Beginner level. No prior Python required — good starting point.

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Beginner·6 min·basics · lists

Lists & Looping

You’ll be able to

Create, index, and modify lists in place
Iterate over lists with for and enumerate()
Add and remove items with append(), pop(), remove()
Sort lists in place and get sorted copies with sorted()

Why this matters

Lists are the default container in every Python codebase, and for loops drive everything from ETL pipelines to ML training epochs. Understanding iteration is the difference between shipping code and copy-pasting Stack Overflow.

Common pitfalls

Mutating a list while iterating: for x in lst: lst.remove(x) skips elements. Iterate over lst[:] or build a new list.
Using list = [1,2,3] as a variable name. It shadows the built-in and breaks list(range(5)) later.
Assuming a = b copies the list. It aliases; use a = b.copy() or a = b[:] to duplicate.

A list holds an ordered sequence of values. You can loop over it directly.

Worth knowing

fruits[0] — first item
fruits.append("kiwi") — add to the end
[expr for x in seq] — list comprehension; concise way to transform a list

Try it

Add a fruit you actually like.
Build a list of fruits whose name has more than 5 letters.

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Start from fruits = ["apple", "banana", "mango"]. Append "kiwi", then print the full list.
Exercise 2
Given nums = [4, 9, 15, 2, 7], use a loop to compute the sum and print just the total. Expected: 37.
Exercise 3
From words = ["apple", "kiwi", "banana", "fig", "mango"], build a list of just the words longer than 4 characters and print it.

← PreviousWhile Loops & break/continue Next →Slicing

Lists & Looping

You’ll be able to

Create, index, and modify lists in place
Iterate over lists with for and enumerate()
Add and remove items with append(), pop(), remove()
Sort lists in place and get sorted copies with sorted()

Why this matters

Common pitfalls

Mutating a list while iterating: for x in lst: lst.remove(x) skips elements. Iterate over lst[:] or build a new list.
Using list = [1,2,3] as a variable name. It shadows the built-in and breaks list(range(5)) later.
Assuming a = b copies the list. It aliases; use a = b.copy() or a = b[:] to duplicate.

A list holds an ordered sequence of values. You can loop over it directly.

Worth knowing

fruits[0] — first item
fruits.append("kiwi") — add to the end
[expr for x in seq] — list comprehension; concise way to transform a list

Try it

Add a fruit you actually like.
Build a list of fruits whose name has more than 5 letters.

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Start from fruits = ["apple", "banana", "mango"]. Append "kiwi", then print the full list.
Exercise 2
Given nums = [4, 9, 15, 2, 7], use a loop to compute the sum and print just the total. Expected: 37.
Exercise 3
From words = ["apple", "kiwi", "banana", "fig", "mango"], build a list of just the words longer than 4 characters and print it.