What Is the Difference Between List Methods Append and Extend

Jinku Hu Sep 17, 2020 Mar 20, 2019 Python Python List
  1. Python List append Method
  2. Python List extend Method
  3. Conclusion of Difference Between append and extend in Python List
What Is the Difference Between List Methods Append and Extend

This article introduces the difference between list append and extend methods in Python.

Python List append Method

append adds the object to the end of the list. The object could be any data type in Python, like list, dictionary or class object.

>>> A = [1, 2]
>>> A.append(3)
>>> A
[1, 2, 3]
>>> A.append([4, 5])
>>> A
[1, 2, 3, [4, 5]]

The length of the list will increase by one after the append is done.

Python List extend Method

extend extends the list by appending elements from the iterable argument. It iterates over the argument and then adds each element to the list. The given argument must be iterable type, like list, otherwise, it will raise TypeError.

>>> A = [1, 2]
>>> A.extend(3)
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    A.extend(3)
TypeError: 'int' object is not iterable

If you want to add 3 to the end of the list, you should firstly put the 3 in a new list.

>>> A = [1, 2]
>>> A.extend([3])
>>> A
[1, 2, 3]

extend method iterates the elements in the iterable object and then adds them one to one to the end of the list.

>>> A = [1, 2]
>>> A.extend([3, 4])
>>> A
[1, 2, 3, 4]

Python extend String Type

Be aware that when the given object is a string type, it will append each character in the string to the list.

>>> A = ["a", "b"]
>>> A.extend("cde")
>>> A
['a', 'b', 'c', 'd', 'e']

Conclusion of Difference Between append and extend in Python List

append adds the given object to the end of the list, therefore the length of the list increases only by 1.

Difference between append and extend in Python - List append

On the other hand, extend adds all the elements in the given object to the end of the list, therefore the length of the list increases by the length of the given object.

Difference between append and extend in Python - List append

Author: Jinku Hu
Jinku Hu avatar Jinku Hu avatar

Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

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