Python Lists With Code Samples and List operations

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+mylist2print(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

The Python Masterclass
Everything you need to know about Python
Python for beginners
Python for finance

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.

 

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