Python list append() method appends an element at the end of the list. It returns None because it does not return any value and modifies the original list.

In the above figure, we are adding an element 10 at the end of the list.

main_list = [19, 18, 21, 29]

print(len(main_list))
# Output: 4

element = 10

main_list.append(element)

print(main_list)
# Output: [19, 18, 21, 29, 10]

print(len(main_list))
# Output: 5

 

The append() method can also accept a collection, which can be a list, dictionary, or any collection object, and adds it as a single element.

Syntax

list.append(element)

Parameters

Argument	Description
element	It represents an item to add to the list. It can be any valid Python object.

Adding a list as a single element

What if we have a list and need to append it to an existing list? It will be added as a single element. So, it will become a nested list.

main_list = [19, 18, 21, 29]

print(len(main_list))
# Output: 4

other_list = [10, 20]

main_list.append(other_list)

print(main_list)
# Output: [19, 18, 21, 29, [10, 20]]

print(len(main_list))
# Output: 5

You can see that before the output, we have a normal list, but after the output, we have a nested list.

Invalid number of arguments

The append() method accepts only one argument at a time, and if you pass multiple arguments in the form of multiple elements, it will throw this error: TypeError: list.append() takes exactly one argument (2 given)

main_list = [19, 18, 21, 29]

print(len(main_list))
# Output: 4

element_a = 10
element_b = 20

main_list.append(element_a, element_b)

# Output: TypeError: list.append() takes exactly one argument (2 given)

To prevent this type of error, always pass a single argument.

Appending multiple elements

To append multiple elements in a Python list, you can use a for loop and, in each iteration, use the append() method.

original_list = [1, 2, 3]
new_items = [4, 5, 6]

for item in new_items:
    original_list.append(item)

print(original_list)

# Output: [1, 2, 3, 4, 5, 6]

Avoid appending in loops for large datasets if order doesn’t matter.

Appending different data types

Let’s add different types of elements to a list one at a time.

original_list = [21]
original_list.append(19)           # Integer
original_list.append("hello")      # String
original_list.append([1, 2, 3])   # List
original_list.append({"key": "value"})  # Dictionary
original_list.append(None)         # NoneType

print(original_list)

# Output: [21, 19, 'hello', [1, 2, 3], {'key': 'value'}, None]

Appending to an empty list

If the input list is empty, and you add an element, it will become the first element at index 0.

empty_list = []

empty_list.append(11)

print(empty_list)

# Output: [11]

Comparison with the list.insert()

The list.insert() method adds an element at a specific position, while the list.append() method adds at the end of the list.

# append() always adds to the end
list1 = [1, 2, 3]
list1.append(4)
print(list1)
# Output: [1, 2, 3, 4]

# insert() adds at specific position
list2 = [1, 2, 3]
list2.insert(1, 'inserted')
print(list2)
# Output: [1, 'inserted', 2, 3]

# insert() at end (equivalent to append)
list3 = [1, 2, 3]
list3.insert(len(list3), 4)
print(list3)
# Output: [1, 2, 3, 4]

That’s all!