There are many built-in types in Python that allow us to group and store multiple items. Python lists are the most versatile among them.
For example, we can use a Python list to store a playlist of songs so that we can easily add, remove, and update songs as needed.
Create a Python List
We create a list by placing elements inside square brackets [], separated by commas. For example,
# a list of three elements
ages = [19, 26, 29]
print(ages)
# Output: [19, 26, 29]
Here, the ages list has three items.
We can store data of different data types in a Python list. For example,
# a list containing strings and numbers
student = ['Jack', 32, 'Computer Science']
print(student)
# an empty list
empty_list = []
print(empty_list)
We can use the built-in list() function to convert other iterables (strings, dictionaries, tuples, etc.) to a list.
x = "axz"
# convert to list
result = list(x)
print(result) # ['a', 'x', 'z']
List Characteristics
Lists are:
- Ordered - They maintain the order of elements.
- Mutable - Items can be changed after creation.
- Allow duplicates - They can contain duplicate values.
Access List Elements
Each element in a list is associated with a number, known as an index.
The index of first item is 0, the index of second item is 1, and so on.
We use these index numbers to access list items. For example,
languages = ['Python', 'Swift', 'C++']
# Access the first element
print(languages[0]) # Python
# Access the third element
print(languages[2]) # C++
More on Accessing List Elements
Python also supports negative indexing. The index of the last element is -1, the second-last element is -2, and so on.
Negative indexing makes it easy to access list items from last.
Let's see an example,
languages = ['Python', 'Swift', 'C++']
# Access item at index 0
print(languages[-1]) # C++
# Access item at index 2
print(languages[-3]) # Python
In Python, it is possible to access a section of items from the list using the slicing operator :. For example,
my_list = ['p', 'r', 'o', 'g', 'r', 'a', 'm']
# items from index 2 to index 4
print(my_list[2:5])
# items from index 5 to end
print(my_list[5:])
# items beginning to end
print(my_list[:])
Output
['o', 'g', 'r'] ['a', 'm'] ['p', 'r', 'o', 'g', 'r', 'a', 'm']
To learn more about slicing, visit Python program to slice lists.
Note: If the specified index does not exist in a list, Python throws the IndexError exception.
Add Elements to a Python List
We use the append() method to add an element to the end of a Python list. For example,
fruits = ['apple', 'banana', 'orange']
print('Original List:', fruits)
# using append method
fruits.append('cherry')
print('Updated List:', fruits)
Output
Original List: ['apple', 'banana', 'orange'] Updated List: ['apple', 'banana', 'orange', 'cherry']
The insert() method adds an element at the specified index. For example,
fruits = ['apple', 'banana', 'orange']
print("Original List:", fruits)
# insert 'cherry' at index 2
fruits.insert(2, 'cherry')
print("Updated List:", fruits)
Output
Original List: ['apple', 'banana', 'orange'] Updated List: ['apple', 'banana', 'cherry', 'orange']
We use the extend() method to add elements to a list from other iterables. For example,
numbers = [1, 3, 5]
print('Numbers:', numbers)
even_numbers = [2, 4, 6]
# adding elements of one list to another
numbers.extend(even_numbers)
print('Updated Numbers:', numbers)
Output
Numbers: [1, 3, 5] Updated Numbers: [1, 3, 5, 2, 4, 6]
Change List Items
We can change the items of a list by assigning new values using the = operator. For example,
colors = ['Red', 'Black', 'Green']
print('Original List:', colors)
# changing the third item to 'Blue'
colors[2] = 'Blue'
print('Updated List:', colors)
Output
Original List: ['Red', 'Black', 'Green'] Updated List: ['Red', 'Black', 'Blue']
Here, we have replaced the element at index 2: 'Green' with 'Blue'.
Remove an Item From a List
We can remove an item from a list using the remove() method. For example,
numbers = [2,4,7,9]
# remove 4 from the list
numbers.remove(4)
print(numbers)
# Output: [2, 7, 9]
The del statement removes one or more items from a list. For example,
names = ['John', 'Eva', 'Laura', 'Nick', 'Jack']
# deleting the second item
del names[1]
print(names)
# deleting items from index 1 to index 3
del names[1: 4]
print(names) # Error! List doesn't exist.
Output
['John', 'Laura', 'Nick', 'Jack'] ['John']
Note: We can also use the del statement to delete the entire list. For example,
names = ['John', 'Eva', 'Laura', 'Nick']
# deleting the entire list
del names
print(names)
Python List Length
We can use the built-in len() function to find the number of elements in a list. For example,
cars = ['BMW', 'Mercedes', 'Tesla']
print('Total Elements: ', len(cars))
# Output: Total Elements: 3
Iterating Through a List
We can use a for loop to iterate over the elements of a list. For example,
fruits = ['apple', 'banana', 'orange']
# iterate through the list
for fruit in fruits:
print(fruit)
Output
apple banana orange
Python List Methods
Python has many useful list methods that make it really easy to work with lists.
| Method | Description |
|---|---|
| append() | Adds an item to the end of the list |
| extend() | Adds items of lists and other iterables to the end of the list |
| insert() | Inserts an item at the specified index |
| remove() | Removes the specified value from the list |
| 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() | Sorts the list in ascending/descending order |
| reverse() | Reverses the item of the list |
| copy() | Returns the shallow copy of the list |
More on Python Lists
List Comprehension is a concise and elegant way to create a list. For example,
# create a list with square values
numbers = [n**2 for n in range(1, 6)]
print(numbers)
# Output: [1, 4, 9, 16, 25]
To learn more, visit Python List Comprehension.
We use the in keyword to check if an item exists in the list. For example,
fruits = ['apple', 'cherry', 'banana']
print('orange' in fruits) # False
print('cherry' in fruits) # True
Here,
- orange is not present in
fruits, so,'orange' in fruitsevaluates toFalse. - cherry is present in
fruits, so,'cherry' in fruitsevaluates toTrue.
Note: Lists are similar to arrays (or dynamic arrays) in other programming languages. When people refer to arrays in Python, they often mean lists, even though there is a numeric array type in Python.
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