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Python List extend() Function

The List extend() method add the elements of an iterable (such as a list, tuple, string, or set) to the end of the current list.

Syntax​

my_list.extend(iterable)

extend() Parameters​

Python List extend() method parameters::

ParameterConditionDescription
iterableRequiredAny iterable (list, tuple, string, or set, etc.)

extend() Return Value​

Python List extend() function does not return anything: it modifies the original list.

Examples​

Example 1: Extending a List with Another List​

For example, let's extend a list with another list:

my_list = [1, 2, 3]
my_list.extend([4, 5, 6])

print(my_list) # Output: [1, 2, 3, 4, 5, 6]

output

[1, 2, 3, 4, 5, 6]

Example 2: Extending a List with a Set​

For example, let's extend a list with a set:

my_list = ['a', 'b', 'c']
my_set = {'d', 'e', 'f'}
my_list.extend(my_set)

print(my_list) # Output: ['a', 'b', 'c', 'd', 'e', 'f']

output

['a', 'b', 'c', 'd', 'e', 'f']

Example 3: Extending a List with a String​

For example, let's extend a list with characters of a string:

my_list = ['Tom', 'Ryan', 'David']
my_list.extend('Anna')

print(my_list) # Output: ['Tom', 'Ryan', 'David', 'A', 'n', 'n', 'a']

output

['Tom', 'Ryan', 'David', 'A', 'n', 'n', 'a']

Example 4: Extending a List with a Single Element​

Of course, you can add a single element to a list: just consider this element as an iterable of a single element (like a list).

my_list = [1, 2]
my_list.extend([3])

print(x) # Output: [1, 2, 3]

output

[1, 2, 3]

extend() method vs append() method​

The extend() method treats its argument as an iterable object.

For example, when you pass a string (iterable object) as an argument, the method adds every character to a list instead of the string.

my_list = ['Tom', 'Ryan', 'David']
my_list.extend('Anna')
print(my_list) # Output: ['Tom', 'Ryan', 'David', 'A', 'n', 'n', 'a']

output

['Tom', 'Ryan', 'David', 'A', 'n', 'n', 'a']

Instead, use append() method:

my_list = ['Tom', 'Ryan', 'David']
my_list.append('Anna')
print(my_list) # Output: ['Tom', 'Ryan', 'David', 'Anna']

output

['Tom', 'Ryan', 'David', 'Anna']
note

The key difference is:

  • append() adds its argument as a single element to the end of a list.
  • extend() iterates over its argument, adding each element to the list, extending the list by however many elements were in the iterable argument

Equivalent Methods to extend() method​

Alternative 1: Zero-length slice​

Specifying a zero-length slice at the end is also equivalent to extend() method.

my_list = ['Tom', 'David', 'Anna']
my_list[len(my_list):] = [1,2,3]

print(my_list) # Output: ['Tom', 'David', 'Anna', 1, 2, 3]

output

['Tom', 'David', 'Anna', 1, 2, 3]

Alternative 2: Concatenation + operator​

Using the concatenation operator + or the augmented assignment operator += on a list is equivalent to using extend().

An example using the concatenation operator + on a list:

my_list = ['Tom', 'David', 'Anna']
my_list = my_list + [1,2,3]

print(my_list) # Output: ['Tom', 'David', 'Anna', 1, 2, 3]

output

['Tom', 'David', 'Anna', 1, 2, 3]

An example using the augmented assignment operator += on a list:

my_list = ['Tom', 'David', 'Anna']
my_list += [1,2,3]

print(my_list) # Output: ['Tom', 'David', 'Anna', 1, 2, 3]

output

['Tom', 'David', 'Anna', 1, 2, 3]

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