When it comes to real-world Python applications, developers might have to add a single item to the existing data structure multiple times. To add an object to an already existing collections type, for instance. This is where the append method in Python shows its value.

Append in Python is a pre-defined method used to add a single item to certain collection types. Without the append method, developers would have to alter the entire collection’s code for adding a single value or item. Its primary use case is seen for a list collection type.

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What Is a List Collection Type, and What Role Does Append Play?

Python offers numerous collection types to store multiple objects and values in a single reference variable. The list is one such collection type. The best thing about lists is that, unlike arrays, you can store values of multiple data types in them. Hence, you can store an integer, a character, a floating number easily in a single list.

The lists’ values are indexed starting from 0 and the last number being n-1, where n is the total values in the list. Since each value has a specific index number, you can add the same value multiple times to the list. Acceptance of the same values and different data types makes lists one of the best collection types to use in Python. Here’s how to create a list:

list_name = [1, “hello”, 2.0 , “world”]

As you can see from the above syntax, you need to separate each value of the list with a comma. You can check the list’s total length with the predefined len() function and any specific value by using the index number. Let’s understand how to create a list, find out the length, and output a single value with the following example.


Besides len(), the list collections type also allows the use of append in Python to add a new item at the end of the list. Let’s look at how to append an item to a list.

Append in Python: Syntax and How to Use It in Lists?

The basic syntax of using the append method in a list is:


As you can see, append in Pyhton takes a single argument, which is the item you want to add to the list. Lists can accept multiple data types; hence, you can add an integer, character, string, another list, or a dictionary with the append method’s help.

Append does not provide any return value. So if you add an item to a list with append, it will not return the list; it will merely alter the list and add the item in the end. Here’s an example to help you understand how to use the append method in a list, add another list, and access the values of the second list.


As you can see from the example, if you add a list to another list with append in Python, it will add the appended list as a single item. If you want to add the second list’s items as individual items to the first list, you need to use the extend() method, but let’s keep it for some other day.

How Append in Python Works With array.array() and collections.deque()

Python provides numerous data structures; array.array() and collections.deque are two of them. Like lists, both these data structures allow you to use the append() method. We will go through each one of them individually and add an object to existing values with the help of append in Python.

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Using Append With array.array()

array.array() is a data structure from the array collection type in Python. Similar to all other programming languages, arrays in Python can accept only a single data type. Hence, you can only add values of similar data type, initialized in array.array(), with the append() method.

The array.array() method takes the following two arguments:

Unicode: It is a required argument that takes a single-character code that determines the data type.

Initializer: It is an optional argument that accepts a list of values of the mentioned data type to initialize the array.

Let’s understand how to use append in array.array() with an example. In this example, we have used “i” as the Unicode. First, we will begin by initializing an array and then use the append method to add an item at the end.


As you can see in the above example, the item at the end of the array  was successfully added with the append method’s help. But when we tried to append a floating integer, the program threw a TypeError. This is because Python cannot convert a floating number to an integer. Similarly, if you try to append any other data type, it will throw an error. One thing to note here is that Python can convert an integer to a floating number. Hence, you can add an integer value to a floating data type array. Let’s look at an example for that too.

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Using Append With collections.deque()

Like lists, collections.deque is also a Python data structure that can accept any data type. The primary difference between the two is that collections.deque can facilitate faster append and pop operations. Hence, you need to select among the two depending on your needs. The name deque stands for a double-ended queue, and it accepts the following arguments:

Iterable: An iterable of multiple values that serve the purpose of initializing the deque.

Maxlen: This argument takes an integer value that defines the maximum length of the deque.

Maxlen is an optional parameter. Defining it will allow the deque only to accept that many inputs. If you try to add more inputs, the item at the opposite end will be automatically discarded. Let’s look at an example to understand how append works in collections.deque().


As you can see from the above example, you can use append in Python’s deques to add any data type object as an input. Apart from the append() method, deques also provide the appendleft() method. Instead of adding an item in the end, the appendleft() method will allow you to add an item at the beginning of the deque.


Append in Python is essential to add a single item at the end of a list, array, deque, or other collection types and data structures on the go. Python has already and is continuing to become one of the most popular programming languages worldwide. Hence, learning about the basic essentials like append in Python is vital if you want to pursue a career in the software development field. You can take the Post Graduate Program in Full Stack Web Development on Simplilearn to learn everything about software development.

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