List methods

2 min read 5 runnable examples Quiz included

Lists come with methods for adding, removing and reorganising items. Most of them change the list in place and return None.

Adding items

Python

tasks = ["email"]
tasks.append("meeting")             # add one item to the end
tasks.insert(0, "coffee")           # insert at a position
tasks.extend(["lunch", "review"])   # add several items
print(tasks)

append adds one item; extend adds each item of another collection. Appending a list puts the whole list in as one item:

Python

a = [1, 2]
a.append([3, 4])
print(a)
b = [1, 2]
b.extend([3, 4])
print(b)

Removing items

Python

queue = ["Asha", "Leo", "Mei", "Raj", "Leo"]

queue.remove("Leo")        # removes the FIRST matching value
print(queue)

last = queue.pop()         # removes and returns the last item
print(last, queue)

first = queue.pop(0)       # removes and returns the item at an index
print(first, queue)

del queue[0]               # delete by index, returns nothing
print(queue)

queue.clear()              # remove everything
print(queue)

remove raises an error if the value is not there, so check with in first if you are unsure.

Sorting

Python

scores = [72, 95, 88, 61]
scores.sort()                      # sorts in place
print(scores)
scores.sort(reverse=True)
print(scores)

words = ["banana", "Apple", "cherry"]
words.sort(key=str.lower)          # sort ignoring case
print(words)

names = ["Mei", "Alexandra", "Leo"]
print(sorted(names, key=len))      # sorted() returns a NEW list
print(names)                       # original unchanged

Reversing

Python

letters = ["a", "b", "c"]
letters.reverse()        # in place
print(letters)
print(list(reversed(letters)))   # new list

Quick reference

Method	Does
`append(x)`	add `x` to the end
`insert(i, x)`	add `x` at index `i`
`extend(items)`	add every item
`remove(x)`	delete the first `x`
`pop()` / `pop(i)`	remove and return last / at `i`
`clear()`	remove everything
`index(x)`	position of the first `x`
`count(x)`	how many times `x` appears
`sort()`	sort in place
`reverse()`	reverse in place
`copy()`	shallow copy

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