[Python] Add elements to list [append, insert, extend, join]

This article show how to add elements to list.

append : Add an element at the end

By using append() method, an element is added to the end of the list.

List.append( element )

Here is an example code.

fruits = ["Apple", "Banana", "Orange"]
print(fruits)
# ['Apple', 'Banana', 'Orange']

fruits.append("Grape")
print(fruits)
# ['Apple', 'Banana', 'Orange', 'Grape']

If list is specified as argument, it is added as an element.

Note that this is not "concatenating".

fruits = ["Apple", "Banana", "Orange"]
print(fruits)
# ['Apple', 'Banana', 'Orange']

num_list = [1, 2, 3]
fruits.append(num_list)
print(fruits)
# ['Apple', 'Banana', 'Orange', [1, 2, 3]]

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insert : Add element at specified position

By using insert() method, an element is inserted at specified position in list.

List.insert( index, element )

Here is an example code.

fruits = ["Apple", "Banana", "Orange"]
print(fruits)
# ['Apple', 'Banana', 'Orange']

fruits.insert(1, "Grape")
print(fruits)
# ['Apple', 'Grape', 'Banana', 'Orange']

Same as "append", if list is specified as argument, it is added as an element.

Note that this is not "concatenating".

fruits = ["Apple", "Banana", "Orange"]
print(fruits)
# ['Apple', 'Banana', 'Orange']

num_list = [1, 2, 3]
fruits.insert(1, num_list)
print(fruits)
# ['Apple', [1, 2, 3], 'Banana', 'Orange']

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extend : Concatenate list at the end

By using extend() method, a list is concatenated at the end of another list.

List.extend( List )

Here is an example code.

fruits = ["Apple", "Banana", "Orange"]
print(fruits)
# ['Apple', 'Banana', 'Orange']

num_list = [1, 2, 3]
fruits.extend(num_list)
print(fruits)
# ['Apple', 'Banana', 'Orange', 1, 2, 3]

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join : Concatenate elements of string

If list contains only elements of string, by using join() function, elements are concatenated into string.

' Delimiter '.join( List )

Here is an example code.

◆No delimiter

example_list = ['I', 'have', 'a', 'pen']
print(example_list)
# ['I', 'have', 'a', 'pen']

example = ''.join(example_list)
print(example)
# Ihaveapen

◆delimiter : ","

example_list = ['I', 'have', 'a', 'pen']
print(example_list)
# ['I', 'have', 'a', 'pen']

example = ' '.join(example_list)
print(example)
# I have a pen

In the following example code, list contains elements of data types other than string.

Before joining, all elements in the list must be converted to string type.

In the following example code, elements are converted to string type by using map function.

example_list = ["Apple", "Banana", "Orange", 100, 200, 300]
print(example_list)
# ['Apple', 'Banana', 'Orange', 100, 200, 300]

example_list_str = map(str, example_list)
example = ','.join(example_list_str)
print(example)
# Apple,Banana,Orange,100,200,300

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"+" : Concatenate list

Also by using "+" operator, lists are combined.

List + List

Here is an example code.

fruits_1 = ["Apple", "Banana", "Orange"]
fruits_2 = ["Grape", "Mango", "Lemon"]

fruits_3 = fruits_1 + fruits_2
print(fruits_3)
# ['Apple', 'Banana', 'Orange', 'Grape', 'Mango', 'Lemon']

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"+=" : Add list

The "+=" operator also combines lists, but rewrites the data in first list.

List += List

Here is an example code.

fruits_1 = ["Apple", "Banana", "Orange"]
fruits_2 = ["Grape", "Mango", "Lemon"]

fruits_1 += fruits_2
print(fruits_1)
# ['Apple', 'Banana', 'Orange', 'Grape', 'Mango', 'Lemon']

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Insert list at specified position using slice

Also by using "Slice", a list is inserted at specified position in list

List[ index : index ] = List

Here is an example code.

fruits_1 = ["Apple", "Banana", "Orange"]
fruits_2 = ["Grape", "Mango", "Lemon"]

fruits_1[1:1] = fruits_2
print(fruits_1)
# ['Apple', 'Grape', 'Mango', 'Lemon', 'Banana', 'Orange']

By using "Slice", elements can also be replaced.

fruits_1 = ["Apple", "Banana", "Orange"]
fruits_2 = ["Grape", "Mango", "Lemon"]

fruits_1[1:2] = fruits_2
print(fruits_1)
# ['Apple', 'Grape', 'Mango', 'Lemon', 'Orange']

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