In my earlier article, I had covered Python numeric and String data types. In this article, I will be covering Python Lists. As the name indicates, you can use a Python list to store a set of values.

Creating a Python List

You can create a list by specifying comma separated values within square brackets. The following code demonstrates this:

mylist = [2,4,'Hello',10.5,"World"]
print (mylist)

As you can see from the code above, a Python list can contain values of different data types. The above code creates a list mylist that has values of type Integer, decimal and String.

Accessing Values in Python Lists

You can access the values in a List via the slice operator. It consists of [] or [:]. You can access Python lists both in the forward as well as backward direction. In the forward direction,lists start from position 0 for the first element in the list. In the backward direction, lists start at position -1 for the last value in the list.

The following code demonstrates this:

mylist = [2,4,'Hello',10.5,"World"] 
print (mylist) 
print(mylist[2]) 
print(mylist[0:2]) 
print(mylist[2:]) 
print(mylist[:3])
print(mylist[-1])
print(mylist[-3:-1])

This code prints the following output:

[2, 4, 'Hello', 10.5, 'World']
Hello
[2, 4]
['Hello', 10.5, 'World']
[2, 4, 'Hello']
World
['Hello', 10.5]

Updating Python Lists

You can update a value in a List. You just need to specify the list name, followed by its position in square brackets and assign it a new value. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
mylist[2] = "horse"
print(mylist)

So this code updates the value at position 2 to “horse”. So this code prints the following output:

['cat', 'dog', 'horse', 'monkey']

Adding to a Python List

There are several ways in which you can add a value to a List.

append

The appendmethod adds a value at the end of the list. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
mylist.append("horse")
print(mylist)

This code adds the value “horse” to the end of the list. So it prints the following output:

['cat', 'dog', 'horse', 'monkey']

insert

The insertmethod adds a value at the specified position. The following code demonstrates this:

mylist= ["cat","dog","cow","monkey"]
mylist.insert(2, "horse")
print(mylist)

This code inserts the value “horse” at position 2. So it prints the following output:

['cat', 'dog', 'horse', 'cow', 'monkey']

Removing from a Python List

There are several ways in which you can remove a value from a List.

remove

The removemethod removes the specified element from the List. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
mylist.remove("dog")
print(mylist)

This code removes the value “dog” from the list. So it prints the following output:

['cat', 'cow', 'monkey']

pop

The popmethod removes the element at the specified index or the last element if no index is specified. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
mylist.pop(1)
print(mylist)

mylist = ["cat","dog","cow","monkey"]
mylist.pop()
print(mylist)

The first code snippet removes the value at position 1 which is dog. In the second code snippet, the index is not specified, so the last value is removed. So this code prints the following output:

['cat', 'cow', 'monkey']
['cat', 'dog', 'cow']

clear

The clearmethod empties a list. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
mylist.clear();
print(mylist)

So this code empties the list. So it prints the following output:

[]

Sorting Python Lists

The sortmethod sorts a list. The following code demonstrates this:

mylist = [5,1,8,12,9];
mylist.sort()
print(mylist)

This code sorts the list in ascending order. So it prints the following output:

[1, 5, 8, 9, 12]

Obtaining Length of a Python List

Python has a built-in function len. This returns the length of the object passed in. You can use this function to obtain the length of a list. The following code demonstrates this:

mylist = ["cat","dog","cow","monkey"]
print(len(mylist))

So this code prints the following output:

4

Concatenating two Python lists

The ‘+‘ operator acts as the concatenation operator. It helps in concatenating Lists. The following code demonstrates this:

mylist1 = ["cat","dog","cow","monkey"]
mylist2 = ["lion","tiger"]
mylist3 = mylist1+mylist2
print(mylist3)

So this code appends the values in myList1and myList2and assigns the resultant list to myList3. So it prints the following output:

['cat', 'dog', 'cow', 'monkey', 'lion', 'tiger']

Further Learning

Conclusion

So in this article, we understood what Python Lists are. We also understood some of the methods that you can use on lists for adding/removing elements from a list, sorting lists, etc.