A Simple Tear Down On List And Arrays

Want to access an array of data without storing them in individual
variables and wasting your memory? This is where the data type list
comes in, 

In this article, I'll help you to use lists in python effectively and give you the difference between a List & an Array

What Is A List?

A List is one of 4 built-in data types created with a [square bracket]. With this data type’s help, you can store an array of items in a List.

The items in the list are ordered, allow duplicate values, and are changeable.

These items are indexed as shown in the image below.

Whenever we add a new item to the list the item will be placed at the
end of the list without changing the order of the items inside the
list. 

Accessing The Items In A List 

The items in the list can be accessed by using the index numbers.

Example Program 

cars = ["Audi", "Toyota", "Suzuki"]
print(cars[0])

Output

Audi

Negative Indexing 

The negative indexing is used to access the items on the lists starting from the end, as shown in the image above. 

Example Program

cars = ["Audi", "Toyota", "Suzuki"]
print(cars[-1])

Output

Suzuki

Access The Items In The List Within A Range Values

You can access the items in the list within the range of the specified start and finish value. 

Example Program

cars = ["Audi", "Toyota", "Suzuki", "Kia"]
print(cars[-3:-1])

Output

[‘Toyota’, ‘Suzuki’]

Checking If An Item Exists In A List 

To determine whether an item is inside a list or not we use the IN keyword. 

Example Program

cars = ["Audi", "Toyota", "Suzuki", "Kia"]
if "Audi" in cars:
    print("Audi is in the list of cars") 

Output

Audi is in the list of cars

Changing The Items In A List 

You can change the value of a specific item by referring to the index number of the item in the list. 

Example Program

cars = ["Audi", "Toyota", "Suzuki", "Kia"]

cars[0] = "Jaguar"

print(cars)

Output

[‘Jaguar’, ‘Toyota’, ‘Suzuki’, ‘Kia’]

Changing A Range of Item Values 

If you want to change a range of item values, you can define a new list by mentioning the range of the items by their index and number. 

Example Program

cars = ["Audi", "Toyota", "Suzuki", "Kia"]

cars[0:2] = ["Jaguar", "Nexa"]

print(cars)

Output

['Jaguar', 'Nexa', 'Suzuki', 'Kia']

Insert A New Item Into A List Using The inset() Function 

You can use the insert() function to insert a new item without replacing any other item in the list. 

Example Program

cars = ["Audi", "Toyota", "Suzuki"]

cars.insert(2, "Kia")

print(cars)

Output

['Audi', 'Toyota', 'Kia', 'Suzuki']

Adding Items to a list Using The Append Function 

You can use the append() method to add an item at the end of the list. 

Example Program

cars = ["Audi", "Toyota", "Suzuki"]

cars.append("Kia")

print(cars)

Output

['Audi', 'Toyota', 'Suzuki', 'Kia']

Extending The List Using The extend() Method 

By using the extend() method you can append the elements from one list to the other. 

Example Program

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

car = ["BMW", "Tata"]

cars.extend(car)

print(cars)

Output

['Audi', 'Toyota', 'Suzuki', 'Kia', 'BMW', 'Tata']

Adding Iterable To A List 

You can also append other iterables like sets, tuples, dictionaries, and lists into a list containing other elements using the extend() method. 

Example Program With A Tuple

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

car = ("BMW", "Tata")

cars.extend(car)

print(cars)

Output

['Audi', 'Toyota', 'Suzuki', 'Kia', 'BMW', 'Tata']

Example Program With A Dictionary

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

car = {"key1":"BMW", "key2":"Tata"}

cars.extend(car)

print(cars)

Output

['Audi', 'Toyota', 'Suzuki', 'Kia', 'key1', 'key2']

Remove List Items 

You can remove an item from a kist by using the methods remove(), pop() and the keyword del. 

Removing A Specified Item From A List 

You can remove an element from a list by using the remove() method 

Example Program

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

cars.remove(“Kia”)

print(cars)

Output

['Audi', 'Toyota', 'Suzuki']

Removing A Specified Index From A List 

You can remove an element from a list by specifying the index number of the item in the list to the method pop(). 

Example Program

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

cars.pop(3)

print(cars)

Output

['Audi', 'Toyota', 'Suzuki']

Example Program Using The del Keyword

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

del.cars[3]

print(cars)

Output

['Audi', 'Toyota', 'Suzuki']

Delete An Entire List 

You can also use the keyword del to delete an entire list without a trace. 

Example Program Using The del Keyword

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

del cars

print(cars)

Output

NameError: name 'cars' is not defined

Clear An Entier List 

You can use the keyword clear() to clear the entire list which will give you an empty list as an output. 

Example Program

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

cars.clear()

print(cars)

Output

[ ]

Looping Through Lists 

You can loop through a list by using for & while Loops as shown in the below examples. 

Example for looping through a list using a For Loop

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

for i in cars:
    print(i) 

Output

Audi

Toyota

Suzuki

Kia

Example for looping through the index number of a list using a For Loop 

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

for i in range(len(cars)):
    print(cars[i]) 

Output

Audi

Toyota

Suzuki

Kia

Example for looping through a list using a While Loop 

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

i = 0

while i < len(cars):
    print(cars[i])
    i = i + 1  

Output

Audi

Toyota

Suzuki

Kia

List Comprehension 

List Comprehension offers shorter syntax where you can create a new list based on the values of an existing list in a single line of code as shown as follows. 

Example For List Comprehension

counting = [i for i in range(5)]
print(counting) 

Output

[0, 1, 2, 3, 4]

A Complex Example For List Comprehension 

cars = ["Audi", "Toyota", "Suzuki",  "Kia"]

updated_cars = [i if i!="Audi" else "Tata" for i in cars]

print(updated_cars)

Output

['Tata', 'Toyota', 'Suzuki', 'Kia']

Sorting Lists 

Using the sort() method you can sort an array of lists. 

Example For Sorting A List Alphanumerically

cars = ["audi", "Toyota", "Suzuki",  "Kia"]

cars.sort()

print(cars)

Output

['Kia', 'Suzuki', 'Toyota', 'audi']

Example For Sorting A List Numerically

num = [9, 2, 3, 4, 5, 1, 7]

num.sort()

print(num)

Output

[1, 2, 3, 4, 5, 7, 9]

Example For Sorting A List Items In Descending Order

num = [9, 2, 3, 4, 5, 1, 7]

num.sort(reverse = True)

print(num)

Output

[9, 7, 5, 4, 3, 2, 1]

Example For Reversing The Items In A List

num = [9, 2, 3, 4, 5, 1, 7]

num.reverse()

print(num)

Output

[7, 1, 5, 4, 3, 2, 9]

Copy Lists 

You might be thinking num_1 = num will do the job but it doesn’t in this case whatever change happened to num_1 will affect the original list named num. 



To avoid the problem mentioned above you can copy a list by using the methods copy() & list() as shown in the example below. 

Example For Using The copy() Method

num = [9, 2, 3, 4, 5, 1, 7]

num_1 = num.copy()

print(num_1)

Output

[9, 2, 3, 4, 5, 1, 7]

Example For Using The list() Method

num = [9, 2, 3, 4, 5, 1, 7]

num_1 = list(num)

print(num_1)

Output

[9, 2, 3, 4, 5, 1, 7]

Joining Lists 

There are several ways to join two or more lists, The examples are mentioned below as follows. 

Example For Concatenating Two Lists

list_1 = [“cat”, “dog”, “ball”]

list_2 = [“1”, “2”, “3”]

list_3 = list_1 + list_2

print(list_3) 

Output

['cat', 'dog', 'ball', '1', '2', '3']

Example For Appending Two Lists

list_1 = [“cat”, “dog”, “ball”]

list_2 = [“1”, “2”, “3”]

for x in list_1:
    list_2.append(x)

print(list_2) 

Output

['1', '2', '3', 'cat', 'dog', 'ball']

Example For Combining Two List Using The extend() Method

list_1 = [“cat”, “dog”, “ball”]

list_2 = [“1”, “2”, “3”]

list_1.extend(list_2)

print(list_1) 

Output

['cat', 'dog', 'ball', '1', '2', '3']

Methods Used In Lists

Difference Between List & Array In Python

Reference Books

Here are the books I’ve used as references for writing this article, please feel free to read them If you don’t want your knowledge to be limited to this article alone.

FAQ