Python List extend() Method

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The Python List extend() method is used to append the contents of an iterable to another list. This iterable can either be an ordered collection of elements (like lists, strings and tuples) or unordered collection of elements (like sets).

The extend() method appends the elements in the iterable individually to the original list. For instance, say we are extending the list ['1', '2'] with the string '34'; the resultant list would be ['1', '2', '3', '4'] instead of ['1', '2', '34']. Therefore, the time complexity of this method is O(n), where n is the length of this iterable.

The length of the final list would be incremented by the number of elements added to the original list.

Syntax

Following is the syntax for the Python List extend() method −

list.extend(seq)

Parameters

• seq − This is the iterable to be appended.

Return Value

This method does not return any value but add the content to existing list.

Example

The following example shows the usage of the Python List extend() method.

aList = [123, 'xyz', 'zara', 'abc', 123]
bList = [2009, 'manni']
aList.extend(bList)
print("Extended List : ", aList)

When we run above program, it produces following result −

Extended List :  [123, 'xyz', 'zara', 'abc', 123, 2009, 'manni']

Example

Let us see an example scenario demonstrating this method. Here, we are creating two lists containing days of the week: ['Mon', 'Tue', 'Wed'] and ['Thu', 'Fri', 'Sat']. The aim of the program is to use the extend() method, in order to append the elements of one list into another, to form one list containing all the days of the week together.

list = ['Mon', 'Tue', 'Wed' ]
print("Existing list:\n",list)

# Extend a list
list.extend(['Thu','Fri','Sat'])
print("Extended a list:\n",list)

Compile and run the program above to obtain the following result −

Existing list:
['Mon', 'Tue', 'Wed']
Extended a list:
['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']

Example

In this example, if we pass a tuple as an argument to this method, the resultant list would be extended by the elements of the tuple.

# Creating a list
nums = [1, 2, 3, 4]
# Displaying the list
print('List Before Appending:')
print(nums)
print()
# Extending the list nums
# 5, 6, 7 will be added at the end of the nums
nums.extend((5, 6, 7))
# Displaying the list
print('List After Appending:')
print(nums)

If we run above program, the following result is displayed −

List Before Appending:
[1, 2, 3, 4]
List After Appending:
[1, 2, 3, 4, 5, 6, 7]

Example

If a string is passed as an argument to this method, each of its character is added as a separate element to the list.

# Creating a list
list1 = ['h', 'i']
# Displaying the list
print('List Before Appending:')
print(list1)
print()
# extending the list list1
# 'h', 'e', 'l', 'l', 'o' will be added at the end of the list1
list1.extend('hello')
# displaying the list
print('List After Appending:')
print(list1)

If you run the above program, you will get the following results.

List Before Appending:
['h', 'i']
List After Appending:
['h', 'i', 'h', 'e', 'l', 'l', 'o']