Difference Between append() and extend() in Python

When you plan to build an application in Python, operating with lists becomes a common Working with lists is a common task in Python, and two frequently used methods for adding elements to a list are append() and extend(). The append() method adds a single item to the end of a list, while extend() adds multiple items from another list or iterable. Though they seem similar, they behave differently and are used in different situations. In this blog, you will understand what the append and extend methods in Python are, along with their key differences and examples for each.

Table of Contents:

• What is the append() Method in Python?
• What is the extend() Method in Python?
• Comparison Table Between append() and extend() in Python
• Performance Implications of extend() vs append()
• Best Practices When Using append() and extend()
• Real-World Use Cases for append() and extend() in Python
• Conclusion
• Difference Between Append and Extend – FAQs

What is the append() Method in Python?

The append() method in Python is used to add a single element at a time to the end of an existing list. The method does not modify existing elements; instead, it adds an item to the list as a single element.

Syntax:

list.append(item)

Example:

Output:

Explanation: Here, 4 is considered as one complete element that gets added at the end of the number list. The previous list had three items, and now it has four items because another one was added because of the append() method.

Example 2: append() with strings

Output:

Explanation: In this case, append() added the entire string “Machine Learning” as a single element at the end of the list.

What is the extend() Method in Python?

The extend() method serves a different purpose in Python. It is used in cases where you want to add several elements from another iterable, which could be a list, a tuple, or a set, to the end of the existing list, one at a time.

Syntax: 

list.extend(iterable)

Example:

Output:

Explanation: Here, instead of adding the whole list [‘d’, ‘e’] as a single element, the extend() method doesn’t add the list as a single element, instead, it unpacks the list to add each item to the list of numbers individually. This proves useful when you want to merge multiple items from an iterable into your list.

Example 2: extend() with a string

Output:

Explanation: Here, since “ML” is a string (an iterable), extend() split it into ‘M’ and ‘L’ and added each character separately to the list.

Comparison Table Between append() and extend() in Python

Summary of Differences Between append() and extend() 

Here, we will give you the essential differences. The Method append() adds one item (whatever the item is) to the end of the list, while extend() takes an iterable and adds each of the elements that are to be added to the list. With append(), even if you give it a list, it will add it as one nested element, while with extend(), you can flatten the incoming iterable into your original list.

Performance Implications of extend() vs append()

Using extend() inside a loop to add multiple elements is more efficient than using append() repeatedly. When you use append(), each item is added one by one, which can be slow and use more memory, especially for large lists. But with extend(), all the items from another list or iterable are added in one go, making it faster and more memory-efficient. So, extend() is the better choice when you need to add many elements at once.

We will demonstrate this by using the Python time module.

For Example:

Output:

Explanation: Here, extend() works significantly faster than using append() in a loop for adding many items. This is because extend() is implemented in C under the hood, meaning its logic is written in C, and it greatly optimizes memory allocation during the operation. On the other hand, append() repeatedly incurs an extra overhead on each case of iteration.

Best Practices When Using append() and extend()

Go through the following tips to avoid bugs and ensure that you utilise the methods to their full potential:

• When adding a single item, use append(): it is good practice to use append(), as extend() will be an inefficient method with less clarity when it comes to adding one item to the list.
• When merging lists or any iterables, use extend(): You can avoid unnecessary nesting and make your output more readable.
• Avoid Unintended List Nesting: If you don’t want to get confused while writing the code, it’s better not to use nested loops for lists or nest lists inside one another. This can occur when you accidentally use append() with another list, which can lead to structures like [[‘a’, ‘b’], ‘c’].
• Always confirm the type of object you’re adding: You can avoid TypeError by passing your iterable to extend() and not an integer value or float.
• You should be explicit in your intentions: You can keep a habit of commenting your code when it is not immediately obvious why you are choosing append() or extend().

Real-World Use Cases for append() and extend() in Python

The section below will implement use cases for both methods, further expanding your capabilities to operate with them.

1. Logging into a site: Tracking individual user actions as they occur.

Example: 

Output:

Explanation: In the example above, each action done by the user is added as an individual log message. Now, since the user is recording one event at a time as a whole string, our best method to implement is append().

2. Comparing courses in a list: Combining multiple course details into one list for comparison.

Example: 

Output:

Explanation: Here, you’re combining two lists. Using extend() unpacks the second list, which is new_products, and adds each item to the first list, which is main_products, individually. When you want to consolidate data from multiple sources, this case is useful.

Conclusion

When working with lists in Python, it’s important to know the difference between append() and extend(). If you want to add just one item to the list, use append(). But if you want to add multiple items from another list or group, use extend(). Understanding these differences will help you write clearer and better code. By following the right practices, you can avoid mistakes and make your list operations easier to understand.

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Difference Between Append and Extend – FAQs