How to Create a List in Python

What you’ll build or solve

You’ll create a list, empty or pre-filled, add items, read items by index, update or remove items, and loop through the list.

When this approach works best

This approach works best when you need:

• An ordered collection, like a set of steps in a workflow or names to display in order.
• A container you can change as your program runs, like adding new items or removing completed ones.
• A simple way to loop over many values, like calculating totals from a series of numbers.

Avoid this approach when:

• You need fast membership checks and no duplicates. Use a set.
• You need key-value lookup. Use a dict.

Prerequisites

• Python 3 installed
• You know how to:
  • Assign a variable: x = 1
  • Print a value: print(x)
  • Run a few lines of Python in a file or an interactive shell

Step-by-step instructions

1) Create a list

Option A: start with values

colors= ["blue","green","red"]
numbers= [10,20,30]

print(colors)
print(numbers)

Option B: start empty

colors= []
print(colors)# []

2) Add items to a list

Add one item with append():

colors= ["blue","green"]
colors.append("red")

print(colors)# ['blue', 'green', 'red']

Add several items with extend():

colors= ["blue"]
colors.extend(["green","red"])

print(colors)# ['blue', 'green', 'red']

What to look for:

append() adds one element. extend() adds each element from another iterable.

3) Read items by index

Indexes start at 0. Negative indexes count from the end.

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

print(colors[0])# blue
print(colors[1])# green
print(colors[-1])# red

If you are not sure an index exists, check the length:

i=3

ifi<len(colors):
print(colors[i])
else:
print("index out of range")

4) Update items

Update an item by index:

colors= ["blue","green","red"]
colors[1]="yellow"

print(colors)# ['blue', 'yellow', 'red']

Insert an item at a specific position:

colors.insert(1,"purple")
print(colors)# ['blue', 'purple', 'yellow', 'red']

5) Remove items

Remove by value with remove():

colors= ["blue","green","red"]
colors.remove("green")

print(colors)# ['blue', 'red']

Remove by index with pop():

colors= ["blue","green","red"]
last=colors.pop()

print(last)# red
print(colors)# ['blue', 'green']

Remove a specific position with pop(index):

colors= ["blue","green","red"]
middle=colors.pop(1)

print(middle)# green
print(colors)# ['blue', 'red']

What to look for:

remove() fails if the value is missing.

pop() fails if the index is out of range.

6) Loop through items

Loop over values:

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

forcolorincolors:
print(color)

Loop with index and value:

fori,colorinenumerate(colors):
print(i,color)

Examples you can copy

1) Build a list by adding items

shopping= []

shopping.append("milk")
shopping.append("bread")
shopping.append("eggs")

print(shopping)

2) Convert a string into a list of words

sentence="Python lists are useful"
words=sentence.split()

print(words)# ['Python', 'lists', 'are', 'useful']

3) Update and remove items from a to-do list

todo= ["email Sam","pay rent","book dentist"]

todo[0]="email Alex"# update
todo.remove("pay rent")# remove by value
done=todo.pop()# remove last item

print("done:",done)
print("left:",todo)

Common mistakes and how to fix them

Mistake 1: Creating a tuple by accident

You might write:

items= (1,2,3)
print(type(items))

Why it breaks:

Parentheses create a tuple, not a list, so you can’t change it the same way.

Correct approach:

items= [1,2,3]
items.append(4)

print(items)# [1, 2, 3, 4]

Mistake 2: Using an index that does not exist

You might write:

colors= ["blue","green","red"]
print(colors[3])

Why it breaks:

Valid indexes are 0 to len(colors) - 1.

Correct approach:

print(colors[-1])# last item

i=3
ifi<len(colors):
print(colors[i])

Mistake 3: Calling remove() on a value that is not in the list

You might write:

colors= ["blue","green","red"]
colors.remove("yellow")

Why it breaks:

remove() raises an error when the value is missing.

Correct approach:

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

if"yellow"incolors:
colors.remove("yellow")

Troubleshooting

If you see IndexError: list index out of range, print len(your_list) and confirm your index is less than the length. Use -1 for the last item.

If you see ValueError: list.remove(x): x not in list, check with if x in your_list: before calling remove().

If you see AttributeError: 'list' object has no attribute 'add', use append() to add one item or extend() to add many.

If you see a tuple type when you expected a list, check for parentheses () instead of brackets [].

If your “list of numbers” prints like ['1', '2'], you have strings. Convert them with int() when you create the list.

Quick recap

• Create a list with [] or with values like ["a", "b"].
• Add one item with append(), add many with extend().
• Read items with list[index], and use 1 for the last item.
• Update with list[index] = value, insert with insert().
• Remove by value with remove(), or by index with pop().
• Loop with for item in list or enumerate(list) when you need indexes.