In Python, lists are used to store multiple items at once. They are similar to arrays in other programming languages. For example,
cars = ['BMW', 'Tesla', 'Ford']
Creating Lists
A list is created by placing items inside [], separated by commas
. For example,
# A list with 3 items
numbers = [1, 2, -5]
# List containing duplicate values
numbers = [1, 2, -5, 2]
# empty list
numbers = []
In Python, a list may contain items of different types. For example,
# A list with 3 items of different types
random_list = [5, 2.5, 'Hello']
A list may also contain another list as an element. For example,
# A list with two items: 5 and [4, 5, 6]
random_list = [5, [4, 5, 6]]
Access List Elements
The items of a list are in order, and we can access individual items of a list using indexes. For example,
cars = ['BMW', 'Tesla', 'Ford']
# access the first item
print(cars[0]) # BMW
# access the third item
print(cars[2]) # Ford
In Python, indexing starts from 0. Meaning,
- the index of the first item is 0
- the index of the second item is 1
- and so on
Hence, cars[0] gives the first item of the
cars list, cars[1] gives the second item, and so on.
Negative Indexing
Python lists also support negative indexing.
- the index of the last item is -1
- the index of the second last item is -2
- and so on
cars = ['BMW', 'Tesla', 'Ford']
# access the last item
print(cars[-1]) # Ford
# access the third last item
print(cars[-3]) # BMW
By the way, if the specified index does not exist in the list, Python throws
the IndexError exception.
cars = ['BMW', 'Tesla', 'Ford']
# trying to access the fourth item
# however, the list only has three items
print(cars[3])
Output
Traceback (most recent call last):
File "<string>", line 4, in <module>
IndexError: list index out of range
Slicing of a List
It is also possible to access a section of items from the list, not just a single item (using the slicing notation). For example,
languages = ['Python', 'JavaScript', 'C++', 'Kotlin']
# first three items -> 0, 1, 2
print(languages[0: 3]) # ['Python', 'JavaScript', 'C++']
# second to last items -> 1, 2, 3
print(languages[1: 4]) # ['JavaScript', 'C++', 'Kotlin']
One thing to remember about list slicing is that the start index is inclusive, whereas the end index is exclusive.
Hence,
-
languages[0: 3]returns a list with items at index 0, 1, and 2 but not 3. -
languages[1: 4]returns a list with items at index 1, 2, and 3 but not 4.
Slicing: Skip Start and End Index
If we use the empty start index, the slicing starts from the beginning of the list. Similarly, if we use the empty end index, the slicing ends at the last index.
languages = ['Python', 'JavaScript', 'C++', 'Kotlin']
# elements from index 0 to 1
print(languages[:2]) # ['Python', 'JavaScript']
# elements from index 2 to last index
print(languages[2:]) # ['C++', 'Kotlin']
Change List Items
Python lists are mutable. Meaning lists are changeable. And, we can change items of a list by assigning new values. For example,
cars = ['BMW', 'Tesla', 'Ford']
# changing the second item to 'Toyota'
cars[1] = 'Toyota'
print(cars) # ['BMW', 'Toyota', 'Ford']
Remember, list indexing starts from 0, not 1. Hence, to change the second
item, we have to assign a new value to cars[1] and not
cars[2].
Delete List
We can remove one or more items from a list using Python's
del statement. The del statement can also be used to delete the
list itself as well.
cars = ['BMW', 'Tesla', 'Ford', 'Toyota']
# deleting the second item
del cars[1]
print(cars) # ['BMW', 'Ford', 'Toyota']
# deleting the last item
del cars[-1]
print(cars) # ['BMW', 'Ford']
# deleting the list
del cars
print(cars) # Error: name 'cars' is not defined
Python List Length
We can find the length of a list using the len() built-in
function. For example,
cars = ['BMW', 'Tesla', 'Ford', 'Toyota']
print(len(cars)) # 4
del cars[0]
print(len(cars)) # 3
Python List Methods
Python has many useful list methods that makes it really easy to work with lists.
| Method | Description |
|---|---|
append() |
add an item to the end of the list |
extend() |
add items of lists and other iterables to the end of the list |
insert() |
inserts an item at the specified index |
remove() |
removes item present at the given index |
pop() |
returns and removes item present at the given index |
clear() |
removes all items from the list |
index() |
returns the index of the first matched item |
count() |
returns the count of the specified item in the list |
sort() |
sort the list in ascending/descending order |
reverse() |
reverses the item of the list |
copy() |
returns the shallow copy of the list |
Iterating through a List
It's really easy to iterate through a list using a for loop.
cars = ['BMW', 'Tesla', 'Ford', 'Toyota']
# iterating through the list
for car in cars:
print(car)
Output
BMW Tesla Ford Toyota
Check if an Item Exists in the List
We can use the in keyword to check if an item exists in the list
or not.
cars = ['BMW', 'Tesla', 'Ford', 'Toyota']
print('Kia' in cars) # False
print('Kia' not in cars) # True
print('BMW' in cars) # True
Python List Comprehension
List comprehension is a concise and elegant way to create lists. For example,
# this code means
# create a list of x*x where
# x takes values from 1 to 5 (range(1, 6))
numbers = [x*x for x in range(1, 6)]
print(numbers) # [1, 4, 9, 16, 25]
Here, this code
numbers = [x*x for x in range(1, 6)]
is equivalent to
numbers = []
for x in range(1, 6):
numbers.append(x * x)
Visit Python List Comprehension.
Python List Summary
In Python, a list is
- collection - can contain multiple items
- ordered - items of a list are in order
- changeable - items of a list can be changed
Recommended Reading: Python Tuple