Python List Append() - How to Append Lists in Python

There are many advantages to using lists in Python. Although lists are similar to arrays in other languages, the main difference between lists and arrays is that lists don’t need to have the same data type. Another major advantage is that lists are mutable, which means we can change a list even after we create it.

Creating Lists in Python

First, let’s talk about how to create a list. In Python, we create lists using square brackets. We separate each item in the list with a comma.

my_list = [‘I’,‘think’,‘Built In’,‘is’,‘number’,‘1’]

type(my_list)

Output:
list

You can see I’ve added both string and numeric data types inside the same list.

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Indexing Lists in Python 

Lists in Python are indexed and have a defined count. The elements in a list are likewise indexed according to a defined sequence with 0 being the first item and n-1 being the last (n is the number of items in a list). Each item in the list has its indexed place.

Our list index starts with 0 and ends with 5, which we can check using the pre-built len() function:

len(my_list)

Output:
6

We can also check each item value based on its index:

my_list[0],my_list[3]

Output:
(‘I’, ‘is’)

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How to Append Lists in Python

The append() method in Python adds a single item to the end of the existing list.

After appending to the list, the size of the list increases by one.

Append Syntax

list_name.append(item)

Append Parameters

The append() method takes a single item as an input parameter and adds that to the end of the list.

Adding Numbers to a List with Append

Let’s look at how to add a new numeric item to a list:

# list of strings

string_list = [‘Built In’,‘Python’,‘Machine Learning’,‘Data Science’]

#adding a new int item to the string_list

string_list.append(1)

#printing appended list

print(string_list)

Output:
[‘Built In’,’Python’,’Machine Learning’,’Data Science’,‘1’]

Adding a List to a List with Append

In addition to adding a strings or numeric data types, we can also append separate lists to a list:

#lets create a new list

new_list = [1,2,3,4,5]

#append this list to our string_list

string_list.append(new_list)

#print the appended list

print(string_list)

Output:
[‘Built In’,’Python’,’Machine Learning’,’Data Science’,’1’,[1,2,3,4,5]]

You can see from the output that a new list is appended at the end of our old list.

To get the whole list as an indexed item, we’ll use:

string_list[5]

Output:
[1,2,3,4,5]

If you want to access the elements from this list you can do that in the same way as you access elements from a 2-D matrix.

string_list[5][1]

Output:
2

If you try to access an item with an index greater than the list index you’ll get an index error.

string_list[6]

Output:
 — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — -
IndexError Traceback (most recent call last)
<ipython-input-14–1d3b13a81e08> in <module>
 — → 1 string_list[6]

IndexError: list index out of range

With these code samples, we can append different data types to a list and access them with ease. This is just one of the many methods we can use in Python lists that make life easier for any Python developer.

Frequently Asked Questions