Python - How To What Is the Difference Between List Methods Append and Extend

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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, 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.

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.