5.2 Lists#
Lists are used to store a collection of objects but are more flexible than tuples. You can create lists using the list function with another iterable object or square brackets []:
list1 = list((1, 2, 3))
print('list1', list1)
list2 = [4, 8, 9]
print('list2', list2)
list1 [1, 2, 3]
list2 [4, 8, 9]
You can access elements of the list by indexing and slicing it:
letters = ['a', 'b', 'c', 'd', 'e']
print('Letters:', letters)
print('First character:', letters[0])
print('Second character:', letters[1])
print('Last character:', letters[-1])
print('Every second character:', letters[::2])
Letters: ['a', 'b', 'c', 'd', 'e']
First character: a
Second character: b
Last character: e
Every second character: ['a', 'c', 'e']
Unlike tuples you can alter the elements of a list after instancing it:
letters = ['a', 'b', 'c', 'd', 'e']
print(letters)
print('Changing the third character')
letters[2] = 'z'
print(letters)
['a', 'b', 'c', 'd', 'e']
Changing the third character
['a', 'b', 'z', 'd', 'e']
You can also assign new values to slices:
letters = ['a', 'b', 'c', 'd', 'e']
print(letters)
print('Changing the first three characters')
letters[:3] = ['x', 'y', 'z']
print(letters)
['a', 'b', 'c', 'd', 'e']
Changing the first three characters
['x', 'y', 'z', 'd', 'e']
Concatenating Lists#
The + operator acts on lists in a similar way to strings, concatenating the two lists:
list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']
print(list1 + list2)
[1, 2, 3, 'a', 'b', 'c']
list.append()#
You can add elements to the end of the list using the .append() method:
letters = ['a', 'b', 'c', 'd', 'e']
print(letters)
print('Appending an additional letter')
letters.append('f')
print(letters)
['a', 'b', 'c', 'd', 'e']
Appending an additional letter
['a', 'b', 'c', 'd', 'e', 'f']
list.insert()#
If you want to insert an element into a specific place in the list you can use the .insert() method. This takes the index and the object you want to add as the arguments:
numbers = [1, 2, 4, 5, 6]
print(numbers)
print('Inserting number 3 at index 2')
numbers.insert(2, 3)
print(numbers)
[1, 2, 4, 5, 6]
Inserting number 3 at index 2
[1, 2, 3, 4, 5, 6]
lists.remove()#
If you want to remove the first instance of an element of a list with a specific value you can use the .remove() method:
numbers = [1, 2, 1, 3, 4]
print(numbers)
print('Removing first 1 from numbers')
numbers.remove(1)
print(numbers)
[1, 2, 1, 3, 4]
Removing first 1 from numbers
[2, 1, 3, 4]
list.pop()#
If you want to retrieve and remove an element at a particular index you can use the .remove() method, which takes the index of the element you want to retrieve as the argument:
numbers = [1, 2, 3, 4, 5]
print(numbers)
print('Retrieving number at index 2:', numbers.pop(2))
print(numbers)
[1, 2, 3, 4, 5]
Retrieving number at index 2: 3
[1, 2, 4, 5]
Unpacking Lists#
Much like with tuples, lists can be unpacked:
a, b, c = [1, 2, 3]
print(a)
print(b)
print(c)
1
2
3
In function calls:
print(*['a', 'b', 'c'])
a b c