Add and Remove Items in a Python List

Add an Item with append()

append() adds one item to the end of a list. You write it after the list's name, with a dot: cart.append("eggs"). A function that belongs to a value like this is called a method.

Think of joining a queue: the new person always goes to the back.

1234cart = ["milk", "bread"]
cart.append("eggs")
print(cart)
print(len(cart))

The rules

• list.append(item) adds the item at the end.
• It changes the list itself. You don't need cart = ... in front.
• It adds one item at a time.

Start empty, then fill up

The empty list from topic 1 is the usual starting point. Make it first, then append:

1234guests = []
guests.append("Sunny")
guests.append("Rocky")
print(guests)

It works with input() from chapter 7, too. Each input() reads one line, and append() stores it:

1234todo = []
todo.append(input())
todo.append(input())
print(todo)

Avoid: storing what append() gives back

123cart = ["milk"]
cart = cart.append("eggs")
print(cart)

The list is gone! append() changes the list and gives back None, the "no value" from chapter 5. Then cart = ... stores that None. Write cart.append("eggs") on its own line.

Avoid: two items in one append()

12cart = ["milk"]
cart.append("eggs", "jam")

An argument is a value you put in the brackets. append() takes exactly one. To add two items, call it twice.

list.append(item) adds one item to the end of the list.

Add an Item Anywhere with insert()

insert() puts an item at any index you choose: list.insert(index, item). The items from that index on move one place to the right.

Think of a friend saving you a spot in a queue. You step in at that spot, and everyone behind you moves back by one.

12345menu = ["tea", "juice"]
menu.insert(0, "water")
print(menu)
menu.insert(2, "coffee")
print(menu)

The rules

• The index comes first, then the item.
• insert(0, item) adds at the front.
• Nothing is replaced. The list gets one item longer.
• An index past the end adds the item at the end, with no error.

123nums = [1, 2]
nums.insert(10, 3)
print(nums)

append() or insert()?

Good: append() when the place doesn't matter, or the item belongs at the end. It's shorter and clearer.

Avoid: insert(len(menu), item). It works, but append(item) says the same thing more simply.

Common mistake: the values swapped

12menu = ["tea"]
menu.insert("coffee", 0)

Python expected a whole number first, the index, but got the string "coffee". Index first, item second.

list.insert(index, item) puts the item at that index and moves the rest to the right.

Remove an Item by Value with remove()

remove() takes an item out of a list by its value: cart.remove("bread"). Python finds the first item equal to that value and removes it.

Think of crossing an item off your shopping list. You look for the word "bread" and strike it out. You don't need to know which line it was on.

123cart = ["milk", "bread", "eggs"]
cart.remove("bread")
print(cart)

The rules

• remove() looks for a value, not an index.
• It removes only the first match.
• The items after it move one place left, so the list gets one item shorter.
• If the value isn't in the list, Python stops with a ValueError.

Only the first match

123votes = ["yes", "no", "yes"]
votes.remove("yes")
print(votes)

The second "yes" stays. To remove it too, call remove() again.

When the value isn't there

12cart = ["milk", "eggs"]
cart.remove("bread")

Don't be scared of this error! The x stands for the value you gave, "bread". Python is saying: "I looked, and it isn't in this list". In topic 5, you'll learn in, which checks first.

Common mistake: remove(0) for the first item

123nums = [5, 0, 7]
nums.remove(0)
print(nums)

remove(0) doesn't remove the first item. It removes the value 0. To remove by position, use pop() or del, in the next lesson.

list.remove(value) removes the first item with that value.

Remove by Index with pop() and del

pop() removes an item by its index and gives it back to you. With no index, it takes the last item. del removes an item by its index and gives nothing back.

Think of a stack of plates. You pop the top plate off, and now it's in your hand, ready to use.

1234plates = ["plate 1", "plate 2", "plate 3"]
top = plates.pop()
print(top)
print(plates)

pop(0) takes the first item. That's how a queue serves the person at the front:

1234queue = ["Sunny", "Rocky", "Lucky"]
first = queue.pop(0)
print(f"Now serving {first}")
print(queue)

When you don't need the item any more, del is enough:

123scores = [10, 0, 30]
del scores[1]
print(scores)

The rules

del is not a method, so there's no dot: write del scores[1], not scores.del(1).

Avoid: popping what isn't there

12empty = []
empty.pop()

An empty list has nothing to pop. An index that's too big fails too: [1, 2].pop(5) gives IndexError: pop index out of range. Check the length with len() first, as you did in topic 2.

pop() removes an item by index and gives it back. del list[i] removes it and gives nothing back.

Practice: Add, remove

Solve these to lock in what you learned in this topic. Each one runs in your browser.

1. 76.Python Program to Add Items to a Shopping ListEasySolve
2. 77.Python Program to Remove a Task by Its NumberMediumSolve